org.mockito

Class Mockito

java.lang.Object

org.mockito.Matchers

org.mockito.Mockito

Direct Known Subclasses:

BDDMockito

public class Mockito
extends Matchers

Mockito library enables mocks creation, verification and stubbing.

This javadoc content is also available on the http://mockito.org web page. All documentation is kept in javadocs because it guarantees consistency between what's on the web and what's in the source code. Also, it makes possible to access documentation straight from the IDE even if you work offline.

Contents

1. Let's verify some behaviour!
2. How about some stubbing?
3. Argument matchers
4. Verifying exact number of invocations / at least once / never
5. Stubbing void methods with exceptions
6. Verification in order
7. Making sure interaction(s) never happened on mock
8. Finding redundant invocations
9. Shorthand for mocks creation - @Mock annotation
10. Stubbing consecutive calls (iterator-style stubbing)
11. Stubbing with callbacks
12. doReturn()|doThrow()|doAnswer()|doNothing()|doCallRealMethod() family of methods
13. Spying on real objects
14. Changing default return values of unstubbed invocations (Since 1.7)
15. Capturing arguments for further assertions (Since 1.8.0)
16. Real partial mocks (Since 1.8.0)
17. Resetting mocks (Since 1.8.0)
18. Troubleshooting & validating framework usage (Since 1.8.0)
19. Aliases for behavior driven development (Since 1.8.0)
20. Serializable mocks (Since 1.8.1)
21. New annotations: @Captor, @Spy, @InjectMocks (Since 1.8.3)
22. Verification with timeout (Since 1.8.5)
23. Automatic instantiation of @Spies, @InjectMocks and constructor injection goodness (Since 1.9.0)
24. One-liner stubs (Since 1.9.0)
25. Verification ignoring stubs (Since 1.9.0)
26. Mocking details (Since 1.9.5)
27. Delegate calls to real instance (Since 1.9.5)
28. MockMaker API (Since 1.9.5)
29. BDD style verification (Since 1.9.8)

Following examples mock a List, because everyone knows its interface (methods like add(), get(), clear() will be used).
You probably wouldn't mock List class 'in real'.

1. Let's verify some behaviour!

 //Let's import Mockito statically so that the code looks clearer
 import static org.mockito.Mockito.*;

 //mock creation
 List mockedList = mock(List.class);

 //using mock object
 mockedList.add("one");
 mockedList.clear();

 //verification
 verify(mockedList).add("one");
 verify(mockedList).clear();
 

Once created, mock will remember all interactions. Then you can selectively verify whatever interaction you are interested in.

2. How about some stubbing?

 //You can mock concrete classes, not only interfaces
 LinkedList mockedList = mock(LinkedList.class);

 //stubbing
 when(mockedList.get(0)).thenReturn("first");
 when(mockedList.get(1)).thenThrow(new RuntimeException());

 //following prints "first"
 System.out.println(mockedList.get(0));

 //following throws runtime exception
 System.out.println(mockedList.get(1));

 //following prints "null" because get(999) was not stubbed
 System.out.println(mockedList.get(999));

 //Although it is possible to verify a stubbed invocation, usually it's just redundant
 //If your code cares what get(0) returns then something else breaks (often before even verify() gets executed).
 //If your code doesn't care what get(0) returns then it should not be stubbed. Not convinced? See here.
 verify(mockedList).get(0);
 

• By default, for all methods that return value, mock returns null, an empty collection or appropriate primitive/primitive wrapper value (e.g: 0, false, ... for int/Integer, boolean/Boolean, ...).
• Stubbing can be overridden: for example common stubbing can go to fixture setup but the test methods can override it. Please note that overridding stubbing is a potential code smell that points out too much stubbing
• Once stubbed, the method will always return stubbed value regardless of how many times it is called.
• Last stubbing is more important - when you stubbed the same method with the same arguments many times. Other words: the order of stubbing matters but it is only meaningful rarely, e.g. when stubbing exactly the same method calls or sometimes when argument matchers are used, etc.

3. Argument matchers

Mockito verifies argument values in natural java style: by using an equals() method. Sometimes, when extra flexibility is required then you might use argument matchers:

 //stubbing using built-in anyInt() argument matcher
 when(mockedList.get(anyInt())).thenReturn("element");

 //stubbing using hamcrest (let's say isValid() returns your own hamcrest matcher):
 when(mockedList.contains(argThat(isValid()))).thenReturn("element");

 //following prints "element"
 System.out.println(mockedList.get(999));

 //you can also verify using an argument matcher
 verify(mockedList).get(anyInt());
 

Argument matchers allow flexible verification or stubbing. Click here to see more built-in matchers and examples of custom argument matchers / hamcrest matchers.

For information solely on custom argument matchers check out javadoc for ArgumentMatcher class.

Be reasonable with using complicated argument matching. The natural matching style using equals() with occasional anyX() matchers tend to give clean & simple tests. Sometimes it's just better to refactor the code to allow equals() matching or even implement equals() method to help out with testing.

Also, read section 15 or javadoc for ArgumentCaptor class. ArgumentCaptor is a special implementation of an argument matcher that captures argument values for further assertions.

Warning on argument matchers:

If you are using argument matchers, all arguments have to be provided by matchers.

E.g: (example shows verification but the same applies to stubbing):

   verify(mock).someMethod(anyInt(), anyString(), eq("third argument"));
   //above is correct - eq() is also an argument matcher

   verify(mock).someMethod(anyInt(), anyString(), "third argument");
   //above is incorrect - exception will be thrown because third argument is given without an argument matcher.
 

Matcher methods like anyObject(), eq() do not return matchers. Internally, they record a matcher on a stack and return a dummy value (usually null). This implementation is due static type safety imposed by java compiler. The consequence is that you cannot use anyObject(), eq() methods outside of verified/stubbed method.

4. Verifying exact number of invocations / at least x / never

 //using mock
 mockedList.add("once");

 mockedList.add("twice");
 mockedList.add("twice");

 mockedList.add("three times");
 mockedList.add("three times");
 mockedList.add("three times");

 //following two verifications work exactly the same - times(1) is used by default
 verify(mockedList).add("once");
 verify(mockedList, times(1)).add("once");

 //exact number of invocations verification
 verify(mockedList, times(2)).add("twice");
 verify(mockedList, times(3)).add("three times");

 //verification using never(). never() is an alias to times(0)
 verify(mockedList, never()).add("never happened");

 //verification using atLeast()/atMost()
 verify(mockedList, atLeastOnce()).add("three times");
 verify(mockedList, atLeast(2)).add("five times");
 verify(mockedList, atMost(5)).add("three times");

 

times(1) is the default. Therefore using times(1) explicitly can be omitted.

5. Stubbing void methods with exceptions

   doThrow(new RuntimeException()).when(mockedList).clear();

   //following throws RuntimeException:
   mockedList.clear();
 

Read more about doThrow|doAnswer family of methods in paragraph 12.

Initially, stubVoid(Object) was used for stubbing voids. Currently stubVoid() is deprecated in favor of doThrow(Throwable). This is because of improved readability and consistency with the family of doAnswer(Answer) methods.

6. Verification in order

 // A. Single mock whose methods must be invoked in a particular order
 List singleMock = mock(List.class);

 //using a single mock
 singleMock.add("was added first");
 singleMock.add("was added second");

 //create an inOrder verifier for a single mock
 InOrder inOrder = inOrder(singleMock);

 //following will make sure that add is first called with "was added first, then with "was added second"
 inOrder.verify(singleMock).add("was added first");
 inOrder.verify(singleMock).add("was added second");

 // B. Multiple mocks that must be used in a particular order
 List firstMock = mock(List.class);
 List secondMock = mock(List.class);

 //using mocks
 firstMock.add("was called first");
 secondMock.add("was called second");

 //create inOrder object passing any mocks that need to be verified in order
 InOrder inOrder = inOrder(firstMock, secondMock);

 //following will make sure that firstMock was called before secondMock
 inOrder.verify(firstMock).add("was called first");
 inOrder.verify(secondMock).add("was called second");

 // Oh, and A + B can be mixed together at will
 

Verification in order is flexible - you don't have to verify all interactions one-by-one but only those that you are interested in testing in order.

Also, you can create InOrder object passing only mocks that are relevant for in-order verification.

7. Making sure interaction(s) never happened on mock

 //using mocks - only mockOne is interacted
 mockOne.add("one");

 //ordinary verification
 verify(mockOne).add("one");

 //verify that method was never called on a mock
 verify(mockOne, never()).add("two");

 //verify that other mocks were not interacted
 verifyZeroInteractions(mockTwo, mockThree);

 

8. Finding redundant invocations

 //using mocks
 mockedList.add("one");
 mockedList.add("two");

 verify(mockedList).add("one");

 //following verification will fail
 verifyNoMoreInteractions(mockedList);
 

A word of warning: Some users who did a lot of classic, expect-run-verify mocking tend to use verifyNoMoreInteractions() very often, even in every test method. verifyNoMoreInteractions() is not recommended to use in every test method. verifyNoMoreInteractions() is a handy assertion from the interaction testing toolkit. Use it only when it's relevant. Abusing it leads to overspecified, less maintainable tests. You can find further reading here.

See also never() - it is more explicit and communicates the intent well.

9. Shorthand for mocks creation - @Mock annotation

• Minimizes repetitive mock creation code.
• Makes the test class more readable.
• Makes the verification error easier to read because the field name is used to identify the mock.

   public class ArticleManagerTest {

       @Mock private ArticleCalculator calculator;
       @Mock private ArticleDatabase database;
       @Mock private UserProvider userProvider;

       private ArticleManager manager;
 

Important! This needs to be somewhere in the base class or a test runner:

 MockitoAnnotations.initMocks(testClass);
 

You can use built-in runner: MockitoJUnitRunner or a rule: MockitoJUnitRule.

Read more here: MockitoAnnotations

10. Stubbing consecutive calls (iterator-style stubbing)

Sometimes we need to stub with different return value/exception for the same method call. Typical use case could be mocking iterators. Original version of Mockito did not have this feature to promote simple mocking. For example, instead of iterators one could use Iterable or simply collections. Those offer natural ways of stubbing (e.g. using real collections). In rare scenarios stubbing consecutive calls could be useful, though:

 when(mock.someMethod("some arg"))
   .thenThrow(new RuntimeException())
   .thenReturn("foo");

 //First call: throws runtime exception:
 mock.someMethod("some arg");

 //Second call: prints "foo"
 System.out.println(mock.someMethod("some arg"));

 //Any consecutive call: prints "foo" as well (last stubbing wins).
 System.out.println(mock.someMethod("some arg"));
 

Alternative, shorter version of consecutive stubbing:

 when(mock.someMethod("some arg"))
   .thenReturn("one", "two", "three");
 

11. Stubbing with callbacks

Allows stubbing with generic Answer interface.

Yet another controversial feature which was not included in Mockito originally. We recommend using simple stubbing with thenReturn() or thenThrow() only. Those two should be just enough to test/test-drive any clean & simple code.

 when(mock.someMethod(anyString())).thenAnswer(new Answer() {
     Object answer(InvocationOnMock invocation) {
         Object[] args = invocation.getArguments();
         Object mock = invocation.getMock();
         return "called with arguments: " + args;
     }
 });

 //Following prints "called with arguments: foo"
 System.out.println(mock.someMethod("foo"));
 

12. doReturn()|doThrow()| doAnswer()|doNothing()|doCallRealMethod() family of methods

Stubbing voids requires different approach from when(Object) because the compiler does not like void methods inside brackets...

doThrow(Throwable) replaces the stubVoid(Object) method for stubbing voids. The main reason is improved readability and consistency with the family of doAnswer() methods.

Use doThrow() when you want to stub a void method with an exception:

   doThrow(new RuntimeException()).when(mockedList).clear();

   //following throws RuntimeException:
   mockedList.clear();
 

You can use doThrow(), doAnswer(), doNothing(), doReturn() and doCallRealMethod() in place of the corresponding call with when(), for any method. It is necessary when you

• stub void methods
• stub methods on spy objects (see below)
• stub the same method more than once, to change the behaviour of a mock in the middle of a test.

but you may prefer to use these methods in place of the alternative with when(), for all of your stubbing calls.

Read more about these methods:

doReturn(Object)

doThrow(Throwable)

doThrow(Class)

doAnswer(Answer)

doNothing()

doCallRealMethod()

13. Spying on real objects

You can create spies of real objects. When you use the spy then the real methods are called (unless a method was stubbed).

Real spies should be used carefully and occasionally, for example when dealing with legacy code.

Spying on real objects can be associated with "partial mocking" concept. Before the release 1.8, Mockito spies were not real partial mocks. The reason was we thought partial mock is a code smell. At some point we found legitimate use cases for partial mocks (3rd party interfaces, interim refactoring of legacy code, the full article is here)

   List list = new LinkedList();
   List spy = spy(list);

   //optionally, you can stub out some methods:
   when(spy.size()).thenReturn(100);

   //using the spy calls *real* methods
   spy.add("one");
   spy.add("two");

   //prints "one" - the first element of a list
   System.out.println(spy.get(0));

   //size() method was stubbed - 100 is printed
   System.out.println(spy.size());

   //optionally, you can verify
   verify(spy).add("one");
   verify(spy).add("two");
 

Important gotcha on spying real objects!

1. Sometimes it's impossible or impractical to use when(Object) for stubbing spies. Therefore when using spies please consider doReturn|Answer|Throw() family of methods for stubbing. Example:

   
      List list = new LinkedList();
      List spy = spy(list);
   
      //Impossible: real method is called so spy.get(0) throws IndexOutOfBoundsException (the list is yet empty)
      when(spy.get(0)).thenReturn("foo");
   
      //You have to use doReturn() for stubbing
      doReturn("foo").when(spy).get(0);
    

2. Mockito *does not* delegate calls to the passed real instance, instead it actually creates a copy of it. So if you keep the real instance and interact with it, don't expect the spied to be aware of those interaction and their effect on real instance state. The corollary is that when an *unstubbed* method is called *on the spy* but *not on the real instance*, you won't see any effects on the real instance.
3. Watch out for final methods. Mockito doesn't mock final methods so the bottom line is: when you spy on real objects + you try to stub a final method = trouble. Also you won't be able to verify those method as well.

14. Changing default return values of unstubbed invocations (Since 1.7)

You can create a mock with specified strategy for its return values. It's quite advanced feature and typically you don't need it to write decent tests. However, it can be helpful for working with legacy systems.

It is the default answer so it will be used only when you don't stub the method call.

   Foo mock = mock(Foo.class, Mockito.RETURNS_SMART_NULLS);
   Foo mockTwo = mock(Foo.class, new YourOwnAnswer());
 

Read more about this interesting implementation of Answer: RETURNS_SMART_NULLS

15. Capturing arguments for further assertions (Since 1.8.0)

Mockito verifies argument values in natural java style: by using an equals() method. This is also the recommended way of matching arguments because it makes tests clean & simple. In some situations though, it is helpful to assert on certain arguments after the actual verification. For example:

   ArgumentCaptor<Person> argument = ArgumentCaptor.forClass(Person.class);
   verify(mock).doSomething(argument.capture());
   assertEquals("John", argument.getValue().getName());
 

Warning: it is recommended to use ArgumentCaptor with verification but not with stubbing. Using ArgumentCaptor with stubbing may decrease test readability because captor is created outside of assert (aka verify or 'then') block. Also it may reduce defect localization because if stubbed method was not called then no argument is captured.

In a way ArgumentCaptor is related to custom argument matchers (see javadoc for ArgumentMatcher class). Both techniques can be used for making sure certain arguments where passed to mocks. However, ArgumentCaptor may be a better fit if:

• custom argument matcher is not likely to be reused
• you just need it to assert on argument values to complete verification

Custom argument matchers via ArgumentMatcher are usually better for stubbing.

16. Real partial mocks (Since 1.8.0)

Finally, after many internal debates & discussions on the mailing list, partial mock support was added to Mockito. Previously we considered partial mocks as code smells. However, we found a legitimate use case for partial mocks - more reading: here

Before release 1.8 spy() was not producing real partial mocks and it was confusing for some users. Read more about spying: here or in javadoc for spy(Object) method.

    //you can create partial mock with spy() method:
    List list = spy(new LinkedList());

    //you can enable partial mock capabilities selectively on mocks:
    Foo mock = mock(Foo.class);
    //Be sure the real implementation is 'safe'.
    //If real implementation throws exceptions or depends on specific state of the object then you're in trouble.
    when(mock.someMethod()).thenCallRealMethod();
  

As usual you are going to read the partial mock warning: Object oriented programming is more less tackling complexity by dividing the complexity into separate, specific, SRPy objects. How does partial mock fit into this paradigm? Well, it just doesn't... Partial mock usually means that the complexity has been moved to a different method on the same object. In most cases, this is not the way you want to design your application.

However, there are rare cases when partial mocks come handy: dealing with code you cannot change easily (3rd party interfaces, interim refactoring of legacy code etc.) However, I wouldn't use partial mocks for new, test-driven & well-designed code.

17. Resetting mocks (Since 1.8.0)

Smart Mockito users hardly use this feature because they know it could be a sign of poor tests. Normally, you don't need to reset your mocks, just create new mocks for each test method.

Instead of reset() please consider writing simple, small and focused test methods over lengthy, over-specified tests. First potential code smell is reset() in the middle of the test method. This probably means you're testing too much. Follow the whisper of your test methods: "Please keep us small & focused on single behavior". There are several threads about it on mockito mailing list.

The only reason we added reset() method is to make it possible to work with container-injected mocks. See issue 55 (here) or FAQ (here).

Don't harm yourself. reset() in the middle of the test method is a code smell (you're probably testing too much).

   List mock = mock(List.class);
   when(mock.size()).thenReturn(10);
   mock.add(1);

   reset(mock);
   //at this point the mock forgot any interactions & stubbing
 

18. Troubleshooting & validating framework usage (Since 1.8.0)

First of all, in case of any trouble, I encourage you to read the Mockito FAQ: http://code.google.com/p/mockito/wiki/FAQ

In case of questions you may also post to mockito mailing list: http://groups.google.com/group/mockito

Next, you should know that Mockito validates if you use it correctly all the time. However, there's a gotcha so please read the javadoc for validateMockitoUsage()

19. Aliases for behavior driven development (Since 1.8.0)

Behavior Driven Development style of writing tests uses //given //when //then comments as fundamental parts of your test methods. This is exactly how we write our tests and we warmly encourage you to do so!

Start learning about BDD here: http://en.wikipedia.org/wiki/Behavior_Driven_Development

The problem is that current stubbing api with canonical role of when word does not integrate nicely with //given //when //then comments. It's because stubbing belongs to given component of the test and not to the when component of the test. Hence BDDMockito class introduces an alias so that you stub method calls with BDDMockito.given(Object) method. Now it really nicely integrates with the given component of a BDD style test!

Here is how the test might look like:

 import static org.mockito.BDDMockito.*;

 Seller seller = mock(Seller.class);
 Shop shop = new Shop(seller);

 public void shouldBuyBread() throws Exception {
   //given
   given(seller.askForBread()).willReturn(new Bread());

   //when
   Goods goods = shop.buyBread();

   //then
   assertThat(goods, containBread());
 }
 

20. Serializable mocks (Since 1.8.1)

Mocks can be made serializable. With this feature you can use a mock in a place that requires dependencies to be serializable.

WARNING: This should be rarely used in unit testing.

The behaviour was implemented for a specific use case of a BDD spec that had an unreliable external dependency. This was in a web environment and the objects from the external dependency were being serialized to pass between layers.

To create serializable mock use MockSettings.serializable():

   List serializableMock = mock(List.class, withSettings().serializable());
 

The mock can be serialized assuming all the normal serialization requirements are met by the class.

Making a real object spy serializable is a bit more effort as the spy(...) method does not have an overloaded version which accepts MockSettings. No worries, you will hardly ever use it.

 List<Object> list = new ArrayList<Object>();
 List<Object> spy = mock(ArrayList.class, withSettings()
                 .spiedInstance(list)
                 .defaultAnswer(CALLS_REAL_METHODS)
                 .serializable());
 

21. New annotations: @Captor, @Spy, @InjectMocks (Since 1.8.3)

Release 1.8.3 brings new annotations that may be helpful on occasion:

• @Captor simplifies creation of ArgumentCaptor - useful when the argument to capture is a nasty generic class and you want to avoid compiler warnings
• @Spy - you can use it instead spy(Object).
• @InjectMocks - injects mock or spy fields into tested object automatically.

Note that @InjectMocks can also be used in combination with the @Spy annotation, it means that Mockito will inject mocks into the partial mock under test. This complexity is another good reason why you should only use partial mocks as a last resort. See point 16 about partial mocks.

All new annotations are *only* processed on MockitoAnnotations.initMocks(Object). Just like for @Mock annotation you can use the built-in runner: MockitoJUnitRunner or rule: MockitoJUnitRule.

22. Verification with timeout (Since 1.8.5)

Allows verifying with timeout. It causes a verify to wait for a specified period of time for a desired interaction rather than fails immediately if had not already happened. May be useful for testing in concurrent conditions.

It feels this feature should be used rarely - figure out a better way of testing your multi-threaded system.

Not yet implemented to work with InOrder verification.

Examples:

   //passes when someMethod() is called within given time span
   verify(mock, timeout(100)).someMethod();
   //above is an alias to:
   verify(mock, timeout(100).times(1)).someMethod();

   //passes when someMethod() is called *exactly* 2 times within given time span
   verify(mock, timeout(100).times(2)).someMethod();

   //passes when someMethod() is called *at least* 2 times within given time span
   verify(mock, timeout(100).atLeast(2)).someMethod();

   //verifies someMethod() within given time span using given verification mode
   //useful only if you have your own custom verification modes.
   verify(mock, new Timeout(100, yourOwnVerificationMode)).someMethod();
 

23. Automatic instantiation of @Spies, @InjectMocks and constructor injection goodness (Since 1.9.0)

Mockito will now try to instantiate @Spy and will instantiate @InjectMocks fields using constructor injection, setter injection, or field injection.

To take advantage of this feature you need to use MockitoAnnotations.initMocks(Object), MockitoJUnitRunner or MockitoJUnitRule.

Read more about available tricks and the rules of injection in the javadoc for InjectMocks

 //instead:
 @Spy BeerDrinker drinker = new BeerDrinker();
 //you can write:
 @Spy BeerDrinker drinker;

 //same applies to @InjectMocks annotation:
 @InjectMocks LocalPub;
 

24. One-liner stubs (Since 1.9.0)

Mockito will now allow you to create mocks when stubbing. Basically, it allows to create a stub in one line of code. This can be helpful to keep test code clean. For example, some boring stub can be created & stubbed at field initialization in a test:

 public class CarTest {
   Car boringStubbedCar = when(mock(Car.class).shiftGear()).thenThrow(EngineNotStarted.class).getMock();

   @Test public void should... {}
 

25. Verification ignoring stubs (Since 1.9.0)

Mockito will now allow to ignore stubbing for the sake of verification. Sometimes useful when coupled with verifyNoMoreInteractions() or verification inOrder(). Helps avoiding redundant verification of stubbed calls - typically we're not interested in verifying stubs.

Warning, ignoreStubs() might lead to overuse of verifyNoMoreInteractions(ignoreStubs(...)); Bear in mind that Mockito does not recommend bombarding every test with verifyNoMoreInteractions() for the reasons outlined in javadoc for verifyNoMoreInteractions(Object...)

Some examples:

 verify(mock).foo();
 verify(mockTwo).bar();

 //ignores all stubbed methods:
 verifyNoMoreInvocations(ignoreStubs(mock, mockTwo));

 //creates InOrder that will ignore stubbed
 InOrder inOrder = inOrder(ignoreStubs(mock, mockTwo));
 inOrder.verify(mock).foo();
 inOrder.verify(mockTwo).bar();
 inOrder.verifyNoMoreInteractions();
 

Advanced examples and more details can be found in javadoc for ignoreStubs(Object...)

26. Mocking details (Since 1.9.5)

To identify whether a particular object is a mock or a spy:

     Mockito.mockingDetails(someObject).isMock();
     Mockito.mockingDetails(someObject).isSpy();
 

Both the MockingDetails.isMock() and MockingDetails.isSpy() methods return boolean. As a spy is just a different kind of mock, isMock() returns true if the object is a spy. In future Mockito versions MockingDetails may grow and provide other useful information about the mock, e.g. invocations, stubbing info, etc.

27. Delegate calls to real instance (Since 1.9.5)

Useful for spies or partial mocks of objects that are difficult to mock or spy using the usual spy API. Possible use cases:

• Final classes but with an interface
• Already custom proxied object
• Special objects with a finalize method, i.e. to avoid executing it 2 times

The difference with the regular spy:

• The regular spy (spy(Object)) contains all state from the spied instance and the methods are invoked on the spy. The spied instance is only used at mock creation to copy the state from. If you call a method on a regular spy and it internally calls other methods on this spy, those calls are remembered for verifications, and they can be effectively stubbed.
• The mock that delegates simply delegates all methods to the delegate. The delegate is used all the time as methods are delegated onto it. If you call a method on a mock that delegates and it internally calls other methods on this mock, those calls are not remembered for verifications, stubbing does not have effect on them, too. Mock that delegates is less powerful than the regular spy but it is useful when the regular spy cannot be created.

See more information in docs for AdditionalAnswers.delegatesTo(Object).

28. MockMaker API (Since 1.9.5)

Driven by requirements and patches from Google Android guys Mockito now offers an extension point that allows replacing the proxy generation engine. By default, Mockito uses cglib to create dynamic proxies.

The extension point is for advanced users that want to extend Mockito. For example, it is now possible to use Mockito for Android testing with a help of dexmaker.

For more details, motivations and examples please refer to the docs for MockMaker.

29. BDD style verification (Since 1.9.8)

Enables Behavior Driven Development (BDD) style verification by starting verification with the BDD then keyword. For more information and an example see BDDMockito.

Field Summary

Fields

Modifier and Type	Field and Description
static Answer<java.lang.Object>	CALLS_REAL_METHODS Optional Answer to be used with mock(Class, Answer)
static Answer<java.lang.Object>	RETURNS_DEEP_STUBS Optional Answer to be used with mock(Class, Answer).
static Answer<java.lang.Object>	RETURNS_DEFAULTS The default Answer of every mock if the mock was not stubbed.
static Answer<java.lang.Object>	RETURNS_MOCKS Optional Answer to be used with mock(Class, Answer)
static Answer<java.lang.Object>	RETURNS_SMART_NULLS Optional Answer to be used with mock(Class, Answer).

Constructor Summary

Constructors

Constructor and Description
Mockito()

Method Summary

Methods

Modifier and Type	Method and Description
static VerificationAfterDelay	after(int millis) Allows verifying over a given period.
static VerificationMode	atLeast(int minNumberOfInvocations) Allows at-least-x verification.
static VerificationMode	atLeastOnce() Allows at-least-once verification.
static VerificationMode	atMost(int maxNumberOfInvocations) Allows at-most-x verification.
static VerificationMode	calls(int wantedNumberOfInvocations) Allows non-greedy verification in order.
static Stubber	doAnswer(Answer answer) Use doAnswer() when you want to stub a void method with generic Answer.
static Stubber	doCallRealMethod() Use doCallRealMethod() when you want to call the real implementation of a method.
static Stubber	doNothing() Use doNothing() for setting void methods to do nothing.
static Stubber	doReturn(java.lang.Object toBeReturned) Use doReturn() in those rare occasions when you cannot use when(Object).
static Stubber	doThrow(java.lang.Class<? extends java.lang.Throwable> toBeThrown) Use doThrow() when you want to stub the void method to throw exception of specified class.
static Stubber	doThrow(java.lang.Throwable toBeThrown) Use doThrow() when you want to stub the void method with an exception.
static java.lang.Object[]	ignoreStubs(java.lang.Object... mocks) Ignores stubbed methods of given mocks for the sake of verification.
static InOrder	inOrder(java.lang.Object... mocks) Creates InOrder object that allows verifying mocks in order.
static <T> T	mock(java.lang.Class<T> classToMock) Creates mock object of given class or interface.
static <T> T	mock(java.lang.Class<T> classToMock, Answer defaultAnswer) Creates mock with a specified strategy for its answers to interactions.
static <T> T	mock(java.lang.Class<T> classToMock, MockSettings mockSettings) Creates a mock with some non-standard settings.
static <T> T	mock(java.lang.Class<T> classToMock, ReturnValues returnValues) Deprecated. Please use mock(Foo.class, defaultAnswer);
static <T> T	mock(java.lang.Class<T> classToMock, java.lang.String name) Specifies mock name.
static MockingDetails	mockingDetails(java.lang.Object toInspect) Returns a MockingDetails instance that enables inspecting a particular object for Mockito related information.
static VerificationMode	never() Alias to times(0), see times(int)
static VerificationMode	only() Allows checking if given method was the only one invoked.
static <T> void	reset(T... mocks) Smart Mockito users hardly use this feature because they know it could be a sign of poor tests.
static <T> T	spy(T object) Creates a spy of the real object.
static <T> DeprecatedOngoingStubbing<T>	stub(T methodCall) Stubs a method call with return value or an exception.
static <T> VoidMethodStubbable<T>	stubVoid(T mock) Deprecated. Use doThrow(Throwable) method for stubbing voids
static VerificationWithTimeout	timeout(long millis) Allows verifying with timeout.
static VerificationMode	times(int wantedNumberOfInvocations) Allows verifying exact number of invocations.
static void	validateMockitoUsage() First of all, in case of any trouble, I encourage you to read the Mockito FAQ: http://code.google.com/p/mockito/wiki/FAQ
static <T> T	verify(T mock) Verifies certain behavior happened once.
static <T> T	verify(T mock, VerificationMode mode) Verifies certain behavior happened at least once / exact number of times / never.
static void	verifyNoMoreInteractions(java.lang.Object... mocks) Checks if any of given mocks has any unverified interaction.
static void	verifyZeroInteractions(java.lang.Object... mocks) Verifies that no interactions happened on given mocks.
static <T> OngoingStubbing<T>	when(T methodCall) Enables stubbing methods.
static MockSettings	withSettings() Allows mock creation with additional mock settings.

Methods inherited from class org.mockito.Matchers

any, any, anyBoolean, anyByte, anyChar, anyCollection, anyCollectionOf, anyDouble, anyFloat, anyInt, anyList, anyListOf, anyLong, anyMap, anyMapOf, anyObject, anySet, anySetOf, anyShort, anyString, anyVararg, argThat, booleanThat, byteThat, charThat, contains, doubleThat, endsWith, eq, eq, eq, eq, eq, eq, eq, eq, eq, floatThat, intThat, isA, isNotNull, isNotNull, isNull, isNull, longThat, matches, notNull, notNull, refEq, same, shortThat, startsWith

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

RETURNS_DEFAULTS

public static final Answer<java.lang.Object> RETURNS_DEFAULTS

The default Answer of every mock if the mock was not stubbed. Typically it just returns some empty value.

Answer can be used to define the return values of unstubbed invocations.

This implementation first tries the global configuration. If there is no global configuration then it uses ReturnsEmptyValues (returns zeros, empty collections, nulls, etc.)

RETURNS_SMART_NULLS

public static final Answer<java.lang.Object> RETURNS_SMART_NULLS

Optional Answer to be used with mock(Class, Answer).

Answer can be used to define the return values of unstubbed invocations.

This implementation can be helpful when working with legacy code. Unstubbed methods often return null. If your code uses the object returned by an unstubbed call you get a NullPointerException. This implementation of Answer returns SmartNull instead of null. SmartNull gives nicer exception message than NPE because it points out the line where unstubbed method was called. You just click on the stack trace.

ReturnsSmartNulls first tries to return ordinary return values (see ReturnsMoreEmptyValues) then it tries to return SmartNull. If the return type is final then plain null is returned.

ReturnsSmartNulls will be probably the default return values strategy in Mockito 2.0.

Example:

   Foo mock = (Foo.class, RETURNS_SMART_NULLS);

   //calling unstubbed method here:
   Stuff stuff = mock.getStuff();

   //using object returned by unstubbed call:
   stuff.doSomething();

   //Above doesn't yield NullPointerException this time!
   //Instead, SmartNullPointerException is thrown.
   //Exception's cause links to unstubbed mock.getStuff() - just click on the stack trace.
 

RETURNS_MOCKS

public static final Answer<java.lang.Object> RETURNS_MOCKS

Optional Answer to be used with mock(Class, Answer)

Answer can be used to define the return values of unstubbed invocations.

This implementation can be helpful when working with legacy code.

ReturnsMocks first tries to return ordinary return values (see ReturnsMoreEmptyValues) then it tries to return mocks. If the return type cannot be mocked (e.g. is final) then plain null is returned.

RETURNS_DEEP_STUBS

public static final Answer<java.lang.Object> RETURNS_DEEP_STUBS

Optional Answer to be used with mock(Class, Answer).

Example that shows how deep stub works:

   Foo mock = mock(Foo.class, RETURNS_DEEP_STUBS);

   // note that we're stubbing a chain of methods here: getBar().getName()
   when(mock.getBar().getName()).thenReturn("deep");

   // note that we're chaining method calls: getBar().getName()
   assertEquals("deep", mock.getBar().getName());
 

WARNING: This feature should rarely be required for regular clean code! Leave it for legacy code. Mocking a mock to return a mock, to return a mock, (...), to return something meaningful hints at violation of Law of Demeter or mocking a value object (a well known anti-pattern).

Good quote I've seen one day on the web: every time a mock returns a mock a fairy dies.

Please note that this answer will return existing mocks that matches the stub. This behavior is ok with deep stubs and allows verification to work on the last mock of the chain.

   when(mock.getBar(anyString()).getThingy().getName()).thenReturn("deep");

   mock.getBar("candy bar").getThingy().getName();

   assertSame(mock.getBar(anyString()).getThingy().getName(), mock.getBar(anyString()).getThingy().getName());
   verify(mock.getBar("candy bar").getThingy()).getName();
   verify(mock.getBar(anyString()).getThingy()).getName();
 

Verification only works with the last mock in the chain. You can use verification modes.

   when(person.getAddress(anyString()).getStreet().getName()).thenReturn("deep");
   when(person.getAddress(anyString()).getStreet(Locale.ITALIAN).getName()).thenReturn("deep");
   when(person.getAddress(anyString()).getStreet(Locale.CHINESE).getName()).thenReturn("deep");

   person.getAddress("the docks").getStreet().getName();
   person.getAddress("the docks").getStreet().getLongName();
   person.getAddress("the docks").getStreet(Locale.ITALIAN).getName();
   person.getAddress("the docks").getStreet(Locale.CHINESE).getName();

   // note that we are actually referring to the very last mock in the stubbing chain.
   InOrder inOrder = inOrder(
       person.getAddress("the docks").getStreet(),
       person.getAddress("the docks").getStreet(Locale.CHINESE),
       person.getAddress("the docks").getStreet(Locale.ITALIAN)
   );
   inOrder.verify(person.getAddress("the docks").getStreet(), times(1)).getName();
   inOrder.verify(person.getAddress("the docks").getStreet()).getLongName();
   inOrder.verify(person.getAddress("the docks").getStreet(Locale.ITALIAN), atLeast(1)).getName();
   inOrder.verify(person.getAddress("the docks").getStreet(Locale.CHINESE)).getName();
 

How deep stub work internally?

   //this:
   Foo mock = mock(Foo.class, RETURNS_DEEP_STUBS);
   when(mock.getBar().getName(), "deep");

   //is equivalent of
   Foo foo = mock(Foo.class);
   Bar bar = mock(Bar.class);
   when(foo.getBar()).thenReturn(bar);
   when(bar.getName()).thenReturn("deep");
 

This feature will not work when any return type of methods included in the chain cannot be mocked (for example: is a primitive or a final class). This is because of java type system.

CALLS_REAL_METHODS

public static final Answer<java.lang.Object> CALLS_REAL_METHODS

Optional Answer to be used with mock(Class, Answer)

Answer can be used to define the return values of unstubbed invocations.

This implementation can be helpful when working with legacy code. When this implementation is used, unstubbed methods will delegate to the real implementation. This is a way to create a partial mock object that calls real methods by default.

As usual you are going to read the partial mock warning: Object oriented programming is more less tackling complexity by dividing the complexity into separate, specific, SRPy objects. How does partial mock fit into this paradigm? Well, it just doesn't... Partial mock usually means that the complexity has been moved to a different method on the same object. In most cases, this is not the way you want to design your application.

However, there are rare cases when partial mocks come handy: dealing with code you cannot change easily (3rd party interfaces, interim refactoring of legacy code etc.) However, I wouldn't use partial mocks for new, test-driven & well-designed code.

Example:

 Foo mock = mock(Foo.class, CALLS_REAL_METHODS);

 // this calls the real implementation of Foo.getSomething()
 value = mock.getSomething();

 when(mock.getSomething()).thenReturn(fakeValue);

 // now fakeValue is returned
 value = mock.getSomething();
 

Constructor Detail

Mockito

public Mockito()

Method Detail

mock

public static <T> T mock(java.lang.Class<T> classToMock)

Creates mock object of given class or interface.

See examples in javadoc for Mockito class

Parameters:

classToMock - class or interface to mock

Returns:

mock object

mock

public static <T> T mock(java.lang.Class<T> classToMock,
         java.lang.String name)

Specifies mock name. Naming mocks can be helpful for debugging - the name is used in all verification errors.

Beware that naming mocks is not a solution for complex code which uses too many mocks or collaborators. If you have too many mocks then refactor the code so that it's easy to test/debug without necessity of naming mocks.

If you use @Mock annotation then you've got naming mocks for free! @Mock uses field name as mock name. Read more.

See examples in javadoc for Mockito class

Parameters:

classToMock - class or interface to mock

name - of the mock

Returns:

mock object

mockingDetails

@Incubating
public static MockingDetails mockingDetails(java.lang.Object toInspect)

Returns a MockingDetails instance that enables inspecting a particular object for Mockito related information. Can be used to find out if given object is a Mockito mock or to find out if a given mock is a spy or mock.

In future Mockito versions MockingDetails may grow and provide other useful information about the mock, e.g. invocations, stubbing info, etc.

Parameters:

toInspect - - object to inspect

Returns:

A MockingDetails instance.

Since:

1.9.5

mock

@Deprecated
public static <T> T mock(java.lang.Class<T> classToMock,
                    ReturnValues returnValues)

Deprecated. Please use mock(Foo.class, defaultAnswer);

Deprecated : Please use mock(Foo.class, defaultAnswer);

See mock(Class, Answer)

Why it is deprecated? ReturnValues is being replaced by Answer for better consistency & interoperability of the framework. Answer interface has been in Mockito for a while and it has the same responsibility as ReturnValues. There's no point in mainting exactly the same interfaces.

Creates mock with a specified strategy for its return values. It's quite advanced feature and typically you don't need it to write decent tests. However it can be helpful when working with legacy systems.

Obviously return values are used only when you don't stub the method call.

   Foo mock = mock(Foo.class, Mockito.RETURNS_SMART_NULLS);
   Foo mockTwo = mock(Foo.class, new YourOwnReturnValues());
 

See examples in javadoc for Mockito class

Parameters:

classToMock - class or interface to mock

returnValues - default return values for unstubbed methods

Returns:

mock object

mock

public static <T> T mock(java.lang.Class<T> classToMock,
         Answer defaultAnswer)

Creates mock with a specified strategy for its answers to interactions. It's quite advanced feature and typically you don't need it to write decent tests. However it can be helpful when working with legacy systems.

It is the default answer so it will be used only when you don't stub the method call.

   Foo mock = mock(Foo.class, RETURNS_SMART_NULLS);
   Foo mockTwo = mock(Foo.class, new YourOwnAnswer());
 

See examples in javadoc for Mockito class

Parameters:

classToMock - class or interface to mock

defaultAnswer - default answer for unstubbed methods

Returns:

mock object

mock

public static <T> T mock(java.lang.Class<T> classToMock,
         MockSettings mockSettings)

Creates a mock with some non-standard settings.

The number of configuration points for a mock grows so we need a fluent way to introduce new configuration without adding more and more overloaded Mockito.mock() methods. Hence MockSettings.

   Listener mock = mock(Listener.class, withSettings()
     .name("firstListner").defaultBehavior(RETURNS_SMART_NULLS));
   );
 

Use it carefully and occasionally. What might be reason your test needs non-standard mocks? Is the code under test so complicated that it requires non-standard mocks? Wouldn't you prefer to refactor the code under test so it is testable in a simple way?

See also withSettings()

See examples in javadoc for Mockito class

Parameters:

classToMock - class or interface to mock

mockSettings - additional mock settings

Returns:

mock object

spy

public static <T> T spy(T object)

Creates a spy of the real object. The spy calls real methods unless they are stubbed.

Real spies should be used carefully and occasionally, for example when dealing with legacy code.

As usual you are going to read the partial mock warning: Object oriented programming is more less tackling complexity by dividing the complexity into separate, specific, SRPy objects. How does partial mock fit into this paradigm? Well, it just doesn't... Partial mock usually means that the complexity has been moved to a different method on the same object. In most cases, this is not the way you want to design your application.

However, there are rare cases when partial mocks come handy: dealing with code you cannot change easily (3rd party interfaces, interim refactoring of legacy code etc.) However, I wouldn't use partial mocks for new, test-driven & well-designed code.

Example:

   List list = new LinkedList();
   List spy = spy(list);

   //optionally, you can stub out some methods:
   when(spy.size()).thenReturn(100);

   //using the spy calls real methods
   spy.add("one");
   spy.add("two");

   //prints "one" - the first element of a list
   System.out.println(spy.get(0));

   //size() method was stubbed - 100 is printed
   System.out.println(spy.size());

   //optionally, you can verify
   verify(spy).add("one");
   verify(spy).add("two");
 

Important gotcha on spying real objects!

1. Sometimes it's impossible or impractical to use when(Object) for stubbing spies. Therefore for spies it is recommended to always use doReturn|Answer|Throw()|CallRealMethod family of methods for stubbing. Example:

   
      List list = new LinkedList();
      List spy = spy(list);
   
      //Impossible: real method is called so spy.get(0) throws IndexOutOfBoundsException (the list is yet empty)
      when(spy.get(0)).thenReturn("foo");
   
      //You have to use doReturn() for stubbing
      doReturn("foo").when(spy).get(0);
    

2. Mockito *does not* delegate calls to the passed real instance, instead it actually creates a copy of it. So if you keep the real instance and interact with it, don't expect the spied to be aware of those interaction and their effect on real instance state. The corollary is that when an *unstubbed* method is called *on the spy* but *not on the real instance*, you won't see any effects on the real instance.
3. Watch out for final methods. Mockito doesn't mock final methods so the bottom line is: when you spy on real objects + you try to stub a final method = trouble. Also you won't be able to verify those method as well.

See examples in javadoc for Mockito class

Note that the spy won't have any annotations of the spied type, because CGLIB won't rewrite them. It may troublesome for code that rely on the spy to have these annotations.

Parameters:

object - to spy on

Returns:

a spy of the real object

stub

public static <T> DeprecatedOngoingStubbing<T> stub(T methodCall)

Stubs a method call with return value or an exception. E.g:

 stub(mock.someMethod()).toReturn(10);

 //you can use flexible argument matchers, e.g:
 stub(mock.someMethod(anyString())).toReturn(10);

 //setting exception to be thrown:
 stub(mock.someMethod("some arg")).toThrow(new RuntimeException());

 //you can stub with different behavior for consecutive method calls.
 //Last stubbing (e.g: toReturn("foo")) determines the behavior for further consecutive calls.
 stub(mock.someMethod("some arg"))
  .toThrow(new RuntimeException())
  .toReturn("foo");
 

Some users find stub() confusing therefore when(Object) is recommended over stub()

   //Instead of:
   stub(mock.count()).toReturn(10);

   //You can do:
   when(mock.count()).thenReturn(10);
 

For stubbing void methods with throwables see: doThrow(Throwable)

Stubbing can be overridden: for example common stubbing can go to fixture setup but the test methods can override it. Please note that overridding stubbing is a potential code smell that points out too much stubbing.

Once stubbed, the method will always return stubbed value regardless of how many times it is called.

Last stubbing is more important - when you stubbed the same method with the same arguments many times.

Although it is possible to verify a stubbed invocation, usually it's just redundant. Let's say you've stubbed foo.bar(). If your code cares what foo.bar() returns then something else breaks(often before even verify() gets executed). If your code doesn't care what get(0) returns then it should not be stubbed. Not convinced? See here.

Parameters:

methodCall - method call

Returns:

DeprecatedOngoingStubbing object to set stubbed value/exception

when

public static <T> OngoingStubbing<T> when(T methodCall)

Enables stubbing methods. Use it when you want the mock to return particular value when particular method is called.

Simply put: "When the x method is called then return y".

when() is a successor of deprecated stub(Object)

Examples:

 when(mock.someMethod()).thenReturn(10);

 //you can use flexible argument matchers, e.g:
 when(mock.someMethod(anyString())).thenReturn(10);

 //setting exception to be thrown:
 when(mock.someMethod("some arg")).thenThrow(new RuntimeException());

 //you can set different behavior for consecutive method calls.
 //Last stubbing (e.g: thenReturn("foo")) determines the behavior of further consecutive calls.
 when(mock.someMethod("some arg"))
  .thenThrow(new RuntimeException())
  .thenReturn("foo");

 //Alternative, shorter version for consecutive stubbing:
 when(mock.someMethod("some arg"))
  .thenReturn("one", "two");
 //is the same as:
 when(mock.someMethod("some arg"))
  .thenReturn("one")
  .thenReturn("two");

 //shorter version for consecutive method calls throwing exceptions:
 when(mock.someMethod("some arg"))
  .thenThrow(new RuntimeException(), new NullPointerException();

 

For stubbing void methods with throwables see: doThrow(Throwable)

Stubbing can be overridden: for example common stubbing can go to fixture setup but the test methods can override it. Please note that overridding stubbing is a potential code smell that points out too much stubbing.

Once stubbed, the method will always return stubbed value regardless of how many times it is called.

Last stubbing is more important - when you stubbed the same method with the same arguments many times.

Although it is possible to verify a stubbed invocation, usually it's just redundant. Let's say you've stubbed foo.bar(). If your code cares what foo.bar() returns then something else breaks(often before even verify() gets executed). If your code doesn't care what get(0) returns then it should not be stubbed. Not convinced? See here.

See examples in javadoc for Mockito class

Parameters:

methodCall - method to be stubbed

Returns:

OngoingStubbing object used to stub fluently. Do not create a reference to this returned object.

verify

public static <T> T verify(T mock)

Verifies certain behavior happened once.

Alias to verify(mock, times(1)) E.g:

   verify(mock).someMethod("some arg");
 

Above is equivalent to:

   verify(mock, times(1)).someMethod("some arg");
 

Arguments passed are compared using equals() method. Read about ArgumentCaptor or ArgumentMatcher to find out other ways of matching / asserting arguments passed.

Although it is possible to verify a stubbed invocation, usually it's just redundant. Let's say you've stubbed foo.bar(). If your code cares what foo.bar() returns then something else breaks(often before even verify() gets executed). If your code doesn't care what get(0) returns then it should not be stubbed. Not convinced? See here.

See examples in javadoc for Mockito class

Parameters:

mock - to be verified

Returns:

mock object itself

verify

public static <T> T verify(T mock,
           VerificationMode mode)

Verifies certain behavior happened at least once / exact number of times / never. E.g:

   verify(mock, times(5)).someMethod("was called five times");

   verify(mock, atLeast(2)).someMethod("was called at least two times");

   //you can use flexible argument matchers, e.g:
   verify(mock, atLeastOnce()).someMethod(anyString());
 

times(1) is the default and can be omitted

Arguments passed are compared using equals() method. Read about ArgumentCaptor or ArgumentMatcher to find out other ways of matching / asserting arguments passed.

Parameters:

mock - to be verified

mode - times(x), atLeastOnce() or never()

Returns:

mock object itself

reset

public static <T> void reset(T... mocks)

Smart Mockito users hardly use this feature because they know it could be a sign of poor tests. Normally, you don't need to reset your mocks, just create new mocks for each test method.

Instead of #reset() please consider writing simple, small and focused test methods over lengthy, over-specified tests. First potential code smell is reset() in the middle of the test method. This probably means you're testing too much. Follow the whisper of your test methods: "Please keep us small & focused on single behavior". There are several threads about it on mockito mailing list.

The only reason we added reset() method is to make it possible to work with container-injected mocks. See issue 55 (here) or FAQ (here).

Don't harm yourself. reset() in the middle of the test method is a code smell (you're probably testing too much).

   List mock = mock(List.class);
   when(mock.size()).thenReturn(10);
   mock.add(1);

   reset(mock);
   //at this point the mock forgot any interactions & stubbing
 

Type Parameters:

T - The Type of the mocks

Parameters:

mocks - to be reset

verifyNoMoreInteractions

public static void verifyNoMoreInteractions(java.lang.Object... mocks)

Checks if any of given mocks has any unverified interaction.

You can use this method after you verified your mocks - to make sure that nothing else was invoked on your mocks.

See also never() - it is more explicit and communicates the intent well.

Stubbed invocations (if called) are also treated as interactions.

A word of warning: Some users who did a lot of classic, expect-run-verify mocking tend to use verifyNoMoreInteractions() very often, even in every test method. verifyNoMoreInteractions() is not recommended to use in every test method. verifyNoMoreInteractions() is a handy assertion from the interaction testing toolkit. Use it only when it's relevant. Abusing it leads to overspecified, less maintainable tests. You can find further reading here.

This method will also detect unverified invocations that occurred before the test method, for example: in setUp(), @Before method or in constructor. Consider writing nice code that makes interactions only in test methods.

Example:

 //interactions
 mock.doSomething();
 mock.doSomethingUnexpected();

 //verification
 verify(mock).doSomething();

 //following will fail because 'doSomethingUnexpected()' is unexpected
 verifyNoMoreInteractions(mock);

 

See examples in javadoc for Mockito class

Parameters:

mocks - to be verified

verifyZeroInteractions

public static void verifyZeroInteractions(java.lang.Object... mocks)

Verifies that no interactions happened on given mocks.

   verifyZeroInteractions(mockOne, mockTwo);
 

This method will also detect invocations that occurred before the test method, for example: in setUp(), @Before method or in constructor. Consider writing nice code that makes interactions only in test methods.

See also never() - it is more explicit and communicates the intent well.

See examples in javadoc for Mockito class

Parameters:

mocks - to be verified

stubVoid

public static <T> VoidMethodStubbable<T> stubVoid(T mock)

Deprecated. Use doThrow(Throwable) method for stubbing voids

   //Instead of:
   stubVoid(mock).toThrow(e).on().someVoidMethod();

   //Please do:
   doThrow(e).when(mock).someVoidMethod();
 

doThrow() replaces stubVoid() because of improved readability and consistency with the family of doAnswer() methods.

Originally, stubVoid() was used for stubbing void methods with exceptions. E.g:

 stubVoid(mock).toThrow(new RuntimeException()).on().someMethod();

 //you can stub with different behavior for consecutive calls.
 //Last stubbing (e.g. toReturn()) determines the behavior for further consecutive calls.
 stubVoid(mock)
   .toThrow(new RuntimeException())
   .toReturn()
   .on().someMethod();
 

See examples in javadoc for Mockito class

Parameters:

mock - to stub

Returns:

stubbable object that allows stubbing with throwable

doThrow

public static Stubber doThrow(java.lang.Throwable toBeThrown)

Use doThrow() when you want to stub the void method with an exception.

Stubbing voids requires different approach from when(Object) because the compiler does not like void methods inside brackets...

Example:

   doThrow(new RuntimeException()).when(mock).someVoidMethod();
 

Parameters:

toBeThrown - to be thrown when the stubbed method is called

Returns:

stubber - to select a method for stubbing

doThrow

public static Stubber doThrow(java.lang.Class<? extends java.lang.Throwable> toBeThrown)

Use doThrow() when you want to stub the void method to throw exception of specified class.

A new exception instance will be created for each method invocation.

Stubbing voids requires different approach from when(Object) because the compiler does not like void methods inside brackets...

Example:

   doThrow(RuntimeException.class).when(mock).someVoidMethod();
 

Parameters:

toBeThrown - to be thrown when the stubbed method is called

Returns:

stubber - to select a method for stubbing

Since:

1.9.0

doCallRealMethod

public static Stubber doCallRealMethod()

Use doCallRealMethod() when you want to call the real implementation of a method.

As usual you are going to read the partial mock warning: Object oriented programming is more less tackling complexity by dividing the complexity into separate, specific, SRPy objects. How does partial mock fit into this paradigm? Well, it just doesn't... Partial mock usually means that the complexity has been moved to a different method on the same object. In most cases, this is not the way you want to design your application.

However, there are rare cases when partial mocks come handy: dealing with code you cannot change easily (3rd party interfaces, interim refactoring of legacy code etc.) However, I wouldn't use partial mocks for new, test-driven & well-designed code.

See also javadoc spy(Object) to find out more about partial mocks. Mockito.spy() is a recommended way of creating partial mocks. The reason is it guarantees real methods are called against correctly constructed object because you're responsible for constructing the object passed to spy() method.

Example:

   Foo mock = mock(Foo.class);
   doCallRealMethod().when(mock).someVoidMethod();

   // this will call the real implementation of Foo.someVoidMethod()
   mock.someVoidMethod();
 

See examples in javadoc for Mockito class

Returns:

stubber - to select a method for stubbing

Since:

1.9.5

doAnswer

public static Stubber doAnswer(Answer answer)

Use doAnswer() when you want to stub a void method with generic Answer.

Stubbing voids requires different approach from when(Object) because the compiler does not like void methods inside brackets...

Example:

  doAnswer(new Answer() {
      public Object answer(InvocationOnMock invocation) {
          Object[] args = invocation.getArguments();
          Mock mock = invocation.getMock();
          return null;
      }})
  .when(mock).someMethod();
 

See examples in javadoc for Mockito class

Parameters:

answer - to answer when the stubbed method is called

Returns:

stubber - to select a method for stubbing

doNothing

public static Stubber doNothing()

Use doNothing() for setting void methods to do nothing. Beware that void methods on mocks do nothing by default! However, there are rare situations when doNothing() comes handy:

1. Stubbing consecutive calls on a void method:

   
      doNothing().
      doThrow(new RuntimeException())
      .when(mock).someVoidMethod();
   
      //does nothing the first time:
      mock.someVoidMethod();
   
      //throws RuntimeException the next time:
      mock.someVoidMethod();
    

2. When you spy real objects and you want the void method to do nothing:

   
      List list = new LinkedList();
      List spy = spy(list);
   
      //let's make clear() do nothing
      doNothing().when(spy).clear();
   
      spy.add("one");
   
      //clear() does nothing, so the list still contains "one"
      spy.clear();
    

See examples in javadoc for Mockito class

Returns:

stubber - to select a method for stubbing

doReturn

public static Stubber doReturn(java.lang.Object toBeReturned)

Use doReturn() in those rare occasions when you cannot use when(Object).

Beware that when(Object) is always recommended for stubbing because it is argument type-safe and more readable (especially when stubbing consecutive calls).

Here are those rare occasions when doReturn() comes handy:

1. When spying real objects and calling real methods on a spy brings side effects

   
      List list = new LinkedList();
      List spy = spy(list);
   
      //Impossible: real method is called so spy.get(0) throws IndexOutOfBoundsException (the list is yet empty)
      when(spy.get(0)).thenReturn("foo");
   
      //You have to use doReturn() for stubbing:
      doReturn("foo").when(spy).get(0);
    

2. Overriding a previous exception-stubbing:

   
      when(mock.foo()).thenThrow(new RuntimeException());
   
      //Impossible: the exception-stubbed foo() method is called so RuntimeException is thrown.
      when(mock.foo()).thenReturn("bar");
   
      //You have to use doReturn() for stubbing:
      doReturn("bar").when(mock).foo();
    

Above scenarios shows a tradeoff of Mockito's elegant syntax. Note that the scenarios are very rare, though. Spying should be sporadic and overriding exception-stubbing is very rare. Not to mention that in general overridding stubbing is a potential code smell that points out too much stubbing.

See examples in javadoc for Mockito class

Parameters:

toBeReturned - to be returned when the stubbed method is called

Returns:

stubber - to select a method for stubbing

inOrder

public static InOrder inOrder(java.lang.Object... mocks)

Creates InOrder object that allows verifying mocks in order.

   InOrder inOrder = inOrder(firstMock, secondMock);

   inOrder.verify(firstMock).add("was called first");
   inOrder.verify(secondMock).add("was called second");
 

Verification in order is flexible - you don't have to verify all interactions one-by-one but only those that you are interested in testing in order.

Also, you can create InOrder object passing only mocks that are relevant for in-order verification.

InOrder verification is 'greedy'. You will hardly every notice it but if you want to find out more search for 'greedy' on the Mockito wiki pages.

As of Mockito 1.8.4 you can verifyNoMoreInvocations() in order-sensitive way. Read more: InOrder.verifyNoMoreInteractions()

See examples in javadoc for Mockito class

Parameters:

mocks - to be verified in order

Returns:

InOrder object to be used to verify in order

ignoreStubs

public static java.lang.Object[] ignoreStubs(java.lang.Object... mocks)

Ignores stubbed methods of given mocks for the sake of verification. Sometimes useful when coupled with verifyNoMoreInteractions() or verification inOrder(). Helps avoiding redundant verification of stubbed calls - typically we're not interested in verifying stubs.

Warning, ignoreStubs() might lead to overuse of verifyNoMoreInteractions(ignoreStubs(...)); Bear in mind that Mockito does not recommend bombarding every test with verifyNoMoreInteractions() for the reasons outlined in javadoc for verifyNoMoreInteractions(Object...) Other words: all *stubbed* methods of given mocks are marked *verified* so that they don't get in a way during verifyNoMoreInteractions().

This method changes the input mocks! This method returns input mocks just for convenience.

Ignored stubs will also be ignored for verification inOrder, including InOrder.verifyNoMoreInteractions(). See the second example.

Example:

  //mocking lists for the sake of the example (if you mock List in real you will burn in hell)
  List mock1 = mock(List.class), mock2 = mock(List.class);

  //stubbing mocks:
  when(mock1.get(0)).thenReturn(10);
  when(mock2.get(0)).thenReturn(20);

  //using mocks by calling stubbed get(0) methods:
  System.out.println(mock1.get(0)); //prints 10
  System.out.println(mock2.get(0)); //prints 20

  //using mocks by calling clear() methods:
  mock1.clear();
  mock2.clear();

  //verification:
  verify(mock1).clear();
  verify(mock2).clear();

  //verifyNoMoreInteractions() fails because get() methods were not accounted for.
  try { verifyNoMoreInteractions(mock1, mock2); } catch (NoInteractionsWanted e);

  //However, if we ignore stubbed methods then we can verifyNoMoreInteractions()
  verifyNoMoreInteractions(ignoreStubs(mock1, mock2));

  //Remember that ignoreStubs() *changes* the input mocks and returns them for convenience.
 

Ignoring stubs can be used with verification in order:

  List list = mock(List.class);
  when(mock.get(0)).thenReturn("foo");

  list.add(0);
  System.out.println(list.get(0)); //we don't want to verify this
  list.clear();

  InOrder inOrder = inOrder(ignoreStubs(list));
  inOrder.verify(list).add(0);
  inOrder.verify(list).clear();
  inOrder.verifyNoMoreInteractions();
 

Parameters:

mocks - input mocks that will be changed

Returns:

the same mocks that were passed in as parameters

Since:

1.9.0

times

public static VerificationMode times(int wantedNumberOfInvocations)

Allows verifying exact number of invocations. E.g:

   verify(mock, times(2)).someMethod("some arg");
 

See examples in javadoc for Mockito class

Parameters:

wantedNumberOfInvocations - wanted number of invocations

Returns:

verification mode

never

public static VerificationMode never()

Alias to times(0), see times(int)

Verifies that interaction did not happen. E.g:

   verify(mock, never()).someMethod();
 

If you want to verify there were NO interactions with the mock check out verifyZeroInteractions(Object...) or verifyNoMoreInteractions(Object...)

See examples in javadoc for Mockito class

Returns:

verification mode

atLeastOnce

public static VerificationMode atLeastOnce()

Allows at-least-once verification. E.g:

   verify(mock, atLeastOnce()).someMethod("some arg");
 

Alias to atLeast(1).

See examples in javadoc for Mockito class

Returns:

verification mode

atLeast

public static VerificationMode atLeast(int minNumberOfInvocations)

Allows at-least-x verification. E.g:

   verify(mock, atLeast(3)).someMethod("some arg");
 

See examples in javadoc for Mockito class

Parameters:

minNumberOfInvocations - minimum number of invocations

Returns:

verification mode

atMost

public static VerificationMode atMost(int maxNumberOfInvocations)

Allows at-most-x verification. E.g:

   verify(mock, atMost(3)).someMethod("some arg");
 

See examples in javadoc for Mockito class

Parameters:

maxNumberOfInvocations - max number of invocations

Returns:

verification mode

calls

public static VerificationMode calls(int wantedNumberOfInvocations)

Allows non-greedy verification in order. For example

   inOrder.verify( mock, calls( 2 )).someMethod( "some arg" );
 

• will not fail if the method is called 3 times, unlike times( 2 )
• will not mark the third invocation as verified, unlike atLeast( 2 )

This verification mode can only be used with in order verification.

Parameters:

wantedNumberOfInvocations - number of invocations to verify

Returns:

verification mode

only

public static VerificationMode only()

Allows checking if given method was the only one invoked. E.g:

   verify(mock, only()).someMethod();
   //above is a shorthand for following 2 lines of code:
   verify(mock).someMethod();
   verifyNoMoreInvocations(mock);
 

See also verifyNoMoreInteractions(Object...)

See examples in javadoc for Mockito class

Returns:

verification mode

timeout

public static VerificationWithTimeout timeout(long millis)

Allows verifying with timeout. It causes a verify to wait for a specified period of time for a desired interaction rather than fails immediately if has not already happened. May be useful for testing in concurrent conditions.

This differs from after() in that after() will wait the full period, unless the final test result is known early (e.g. if a never() fails), whereas timeout() will stop early as soon as verification passes, producing different behaviour when used with times(2), for example, which can pass and then later fail. In that case, timeout would pass as soon as times(2) passes, whereas after would run until times(2) failed, and then fail.

It feels this feature should be used rarely - figure out a better way of testing your multi-threaded system

Not yet implemented to work with InOrder verification.

   //passes when someMethod() is called within given time span
   verify(mock, timeout(100)).someMethod();
   //above is an alias to:
   verify(mock, timeout(100).times(1)).someMethod();

   //passes as soon as someMethod() has been called 2 times before the given timeout
   verify(mock, timeout(100).times(2)).someMethod();

   //equivalent: this also passes as soon as someMethod() has been called 2 times before the given timeout
   verify(mock, timeout(100).atLeast(2)).someMethod();

   //verifies someMethod() within given time span using given verification mode
   //useful only if you have your own custom verification modes.
   verify(mock, new Timeout(100, yourOwnVerificationMode)).someMethod();
 

See examples in javadoc for Mockito class

Parameters:

millis - - time span in milliseconds

Returns:

verification mode

after

public static VerificationAfterDelay after(int millis)

Allows verifying over a given period. It causes a verify to wait for a specified period of time for a desired interaction rather than failing immediately if has not already happened. May be useful for testing in concurrent conditions.

This differs from timeout() in that after() will wait the full period, whereas timeout() will stop early as soon as verification passes, producing different behaviour when used with times(2), for example, which can pass and then later fail. In that case, timeout would pass as soon as times(2) passes, whereas after would run the full time, which point it will fail, as times(2) has failed.

It feels this feature should be used rarely - figure out a better way of testing your multi-threaded system

Not yet implemented to work with InOrder verification.

   //passes after 100ms, if someMethod() has only been called once at that time.
   verify(mock, after(100)).someMethod();
   //above is an alias to:
   verify(mock, after(100).times(1)).someMethod();

   //passes if someMethod() is called *exactly* 2 times after the given timespan
   verify(mock, after(100).times(2)).someMethod();

   //passes if someMethod() has not been called after the given timespan
   verify(mock, after(100).never()).someMethod();

   //verifies someMethod() after a given time span using given verification mode
   //useful only if you have your own custom verification modes.
   verify(mock, new After(100, yourOwnVerificationMode)).someMethod();
 

See examples in javadoc for Mockito class

Parameters:

millis - - time span in milliseconds

Returns:

verification mode

validateMockitoUsage

public static void validateMockitoUsage()

First of all, in case of any trouble, I encourage you to read the Mockito FAQ: http://code.google.com/p/mockito/wiki/FAQ

In case of questions you may also post to mockito mailing list: http://groups.google.com/group/mockito

validateMockitoUsage() explicitly validates the framework state to detect invalid use of Mockito. However, this feature is optional because Mockito validates the usage all the time... but there is a gotcha so read on.

Examples of incorrect use:

 //Oops, thenReturn() part is missing:
 when(mock.get());

 //Oops, verified method call is inside verify() where it should be on the outside:
 verify(mock.execute());

 //Oops, missing method to verify:
 verify(mock);
 

Mockito throws exceptions if you misuse it so that you know if your tests are written correctly. The gotcha is that Mockito does the validation next time you use the framework (e.g. next time you verify, stub, call mock etc.). But even though the exception might be thrown in the next test, the exception message contains a navigable stack trace element with location of the defect. Hence you can click and find the place where Mockito was misused.

Sometimes though, you might want to validate the framework usage explicitly. For example, one of the users wanted to put validateMockitoUsage() in his @After method so that he knows immediately when he misused Mockito. Without it, he would have known about it not sooner than next time he used the framework. One more benefit of having validateMockitoUsage() in @After is that jUnit runner and rule will always fail in the test method with defect whereas ordinary 'next-time' validation might fail the next test method. But even though JUnit might report next test as red, don't worry about it and just click at navigable stack trace element in the exception message to instantly locate the place where you misused mockito.

Both built-in runner: MockitoJUnitRunner and rule: MockitoJUnitRule do validateMockitoUsage() after each test method.

Bear in mind that usually you don't have to validateMockitoUsage() and framework validation triggered on next-time basis should be just enough, mainly because of enhanced exception message with clickable location of defect. However, I would recommend validateMockitoUsage() if you already have sufficient test infrastructure (like your own runner or base class for all tests) because adding a special action to @After has zero cost.

See examples in javadoc for Mockito class

withSettings

public static MockSettings withSettings()

Allows mock creation with additional mock settings.

Don't use it too often. Consider writing simple tests that use simple mocks. Repeat after me: simple tests push simple, KISSy, readable & maintainable code. If you cannot write a test in a simple way - refactor the code under test.

Examples of mock settings:

   //Creates mock with different default answer & name
   Foo mock = mock(Foo.class, withSettings()
       .defaultAnswer(RETURNS_SMART_NULLS)
       .name("cool mockie"));

   //Creates mock with different default answer, descriptive name and extra interfaces
   Foo mock = mock(Foo.class, withSettings()
       .defaultAnswer(RETURNS_SMART_NULLS)
       .name("cool mockie")
       .extraInterfaces(Bar.class));
 

MockSettings has been introduced for two reasons. Firstly, to make it easy to add another mock settings when the demand comes. Secondly, to enable combining different mock settings without introducing zillions of overloaded mock() methods.

See javadoc for MockSettings to learn about possible mock settings.

Returns:

mock settings instance with defaults.