Assertions

Class used via an implicit conversion to enable two objects to be compared with === and !== with a Boolean result and an enforced type constraint between two object types. For example:

assert(a === b)
assert(c !== d)

You can also check numeric values against another with a tolerance. Here are some examples:

assert(a === (2.0 +- 0.1))
assert(c !== (2.0 +- 0.1))

Class used via an implicit conversion to enable any two objects to be compared with === and !== with a Boolean result and no enforced type constraint between two object types. For example:

assert(a === b)
assert(c !== d)

You can also check numeric values against another with a tolerance. Here are some examples:

assert(a === (2.0 +- 0.1))
assert(c !== (2.0 +- 0.1))

Assert that a boolean condition is true. If the condition is true, this method returns normally. Else, it throws TestFailedException.

This method is implemented in terms of a Scala macro that will generate a more helpful error message for expressions of this form:

• assert(a == b)

• assert(a != b)

• assert(a === b)

• assert(a !== b)

• assert(a > b)

• assert(a >= b)

• assert(a < b)

• assert(a <= b)

• assert(a startsWith "prefix")

• assert(a endsWith "postfix")

• assert(a contains "something")

• assert(a eq b)

• assert(a ne b)

• assert(a > 0 && b > 5)

• assert(a > 0 || b > 5)

• assert(a.isEmpty)

• assert(!a.isEmpty)

• assert(a.isInstanceOf[String])

• assert(a.length == 8)

• assert(a.size == 8)

• assert(a.exists(_ == 8))

At this time, any other form of expression will get a TestFailedException with message saying the given expression was false. In the future, we will enhance this macro to give helpful error messages in more situations. In ScalaTest 2.0, however, this behavior was sufficient to allow the === that returns Boolean to be the default in tests. This makes === consistent between tests and production code.

Assert that a boolean condition, described in String message, is true. If the condition is true, this method returns normally. Else, it throws TestFailedException with a helpful error message appended with the String obtained by invoking toString on the specified clue as the exception's detail message.

This method is implemented in terms of a Scala macro that will generate a more helpful error message for expressions of this form:

• assert(a == b, "a good clue")

• assert(a != b, "a good clue")

• assert(a === b, "a good clue")

• assert(a !== b, "a good clue")

• assert(a > b, "a good clue")

• assert(a >= b, "a good clue")

• assert(a < b, "a good clue")

• assert(a <= b, "a good clue")

• assert(a startsWith "prefix", "a good clue")

• assert(a endsWith "postfix", "a good clue")

• assert(a contains "something", "a good clue")

• assert(a eq b, "a good clue")

• assert(a ne b, "a good clue")

• assert(a > 0 && b > 5, "a good clue")

• assert(a > 0 || b > 5, "a good clue")

• assert(a.isEmpty, "a good clue")

• assert(!a.isEmpty, "a good clue")

• assert(a.isInstanceOf[String], "a good clue")

• assert(a.length == 8, "a good clue")

• assert(a.size == 8, "a good clue")

• assert(a.exists(_ == 8), "a good clue")

At this time, any other form of expression will just get a TestFailedException with message saying the given expression was false. In the future, we will enhance this macro to give helpful error messages in more situations. In ScalaTest 2.0, however, this behavior was sufficient to allow the === that returns Boolean to be the default in tests. This makes === consistent between tests and production code.

Asserts that a given string snippet of code passes both the Scala parser and type checker.

You can use this to make sure a snippet of code compiles:

assertCompiles("val a: Int = 1")

Although assertCompiles is implemented with a macro that determines at compile time whether the snippet of code represented by the passed string compiles, errors (i.e., snippets of code that do not compile) are reported as test failures at runtime.

Asserts that a given string snippet of code does not pass either the Scala parser or type checker.

Often when creating libraries you may wish to ensure that certain arrangements of code that represent potential “user errors” do not compile, so that your library is more error resistant. ScalaTest's Assertions trait includes the following syntax for that purpose:

assertDoesNotCompile("val a: String = \"a string")

Although assertDoesNotCompile is implemented with a macro that determines at compile time whether the snippet of code represented by the passed string doesn't compile, errors (i.e., snippets of code that do compile) are reported as test failures at runtime.

Note that the difference between assertTypeError and assertDoesNotCompile is that assertDoesNotCompile will succeed if the given code does not compile for any reason, whereas assertTypeError will only succeed if the given code does not compile because of a type error. If the given code does not compile because of a syntax error, for example, assertDoesNotCompile will return normally but assertTypeError will throw a TestFailedException.

Assert that the value passed as expected equals the value passed as actual. If the actual equals the expected (as determined by ==), assertResult returns normally. Else, if actual is not equal to expected, assertResult throws a TestFailedException whose detail message includes the expected and actual values, as well as the String obtained by invoking toString on the passed clue.

Assert that the value passed as expected equals the value passed as actual. If the actual value equals the expected value (as determined by ==), assertResult returns normally. Else, assertResult throws a TestFailedException whose detail message includes the expected and actual values.

Ensure that an expected exception is thrown by the passed function value. The thrown exception must be an instance of the type specified by the type parameter of this method. This method invokes the passed function. If the function throws an exception that's an instance of the specified type, this method returns Succeeded. Else, whether the passed function returns normally or completes abruptly with a different exception, this method throws TestFailedException.

Note that the type specified as this method's type parameter may represent any subtype of AnyRef, not just Throwable or one of its subclasses. In Scala, exceptions can be caught based on traits they implement, so it may at times make sense to specify a trait that the intercepted exception's class must mix in. If a class instance is passed for a type that could not possibly be used to catch an exception (such as String, for example), this method will complete abruptly with a TestFailedException.

Also note that the difference between this method and intercept is that this method does not return the expected exception, so it does not let you perform further assertions on that exception. Instead, this method returns Succeeded, which means it can serve as the last statement in an async- or safe-style suite. It also indicates to the reader of the code that nothing further is expected about the thrown exception other than its type. The recommended usage is to use assertThrows by default, intercept only when you need to inspect the caught exception further.

Asserts that a given string snippet of code does not pass the Scala type checker, failing if the given snippet does not pass the Scala parser.

Often when creating libraries you may wish to ensure that certain arrangements of code that represent potential “user errors” do not compile, so that your library is more error resistant. ScalaTest's Assertions trait includes the following syntax for that purpose:

assertTypeError("val a: String = 1")

Although assertTypeError is implemented with a macro that determines at compile time whether the snippet of code represented by the passed string type checks, errors (i.e., snippets of code that do type check) are reported as test failures at runtime.

Note that the difference between assertTypeError and assertDoesNotCompile is that assertDoesNotCompile will succeed if the given code does not compile for any reason, whereas assertTypeError will only succeed if the given code does not compile because of a type error. If the given code does not compile because of a syntax error, for example, assertDoesNotCompile will return normally but assertTypeError will throw a TestFailedException.

Assume that a boolean condition is true. If the condition is true, this method returns normally. Else, it throws TestCanceledException.

This method is implemented in terms of a Scala macro that will generate a more helpful error message for expressions of this form:

• assume(a == b)

• assume(a != b)

• assume(a === b)

• assume(a !== b)

• assume(a > b)

• assume(a >= b)

• assume(a < b)

• assume(a <= b)

• assume(a startsWith "prefix")

• assume(a endsWith "postfix")

• assume(a contains "something")

• assume(a eq b)

• assume(a ne b)

• assume(a > 0 && b > 5)

• assume(a > 0 || b > 5)

• assume(a.isEmpty)

• assume(!a.isEmpty)

• assume(a.isInstanceOf[String])

• assume(a.length == 8)

• assume(a.size == 8)

• assume(a.exists(_ == 8))

At this time, any other form of expression will just get a TestCanceledException with message saying the given expression was false. In the future, we will enhance this macro to give helpful error messages in more situations. In ScalaTest 2.0, however, this behavior was sufficient to allow the === that returns Boolean to be the default in tests. This makes === consistent between tests and production code.

Assume that a boolean condition, described in String message, is true. If the condition is true, this method returns normally. Else, it throws TestCanceledException with a helpful error message appended with String obtained by invoking toString on the specified clue as the exception's detail message.

This method is implemented in terms of a Scala macro that will generate a more helpful error message for expressions of this form:

• assume(a == b, "a good clue")

• assume(a != b, "a good clue")

• assume(a === b, "a good clue")

• assume(a !== b, "a good clue")

• assume(a > b, "a good clue")

• assume(a >= b, "a good clue")

• assume(a < b, "a good clue")

• assume(a <= b, "a good clue")

• assume(a startsWith "prefix", "a good clue")

• assume(a endsWith "postfix", "a good clue")

• assume(a contains "something", "a good clue")

• assume(a eq b, "a good clue")

• assume(a ne b, "a good clue")

• assume(a > 0 && b > 5, "a good clue")

• assume(a > 0 || b > 5, "a good clue")

• assume(a.isEmpty, "a good clue")

• assume(!a.isEmpty, "a good clue")

• assume(a.isInstanceOf[String], "a good clue")

• assume(a.length == 8, "a good clue")

• assume(a.size == 8, "a good clue")

• assume(a.exists(_ == 8), "a good clue")

At this time, any other form of expression will just get a TestCanceledException with message saying the given expression was false. In the future, we will enhance this macro to give helpful error messages in more situations. In ScalaTest 2.0, however, this behavior was sufficient to allow the === that returns Boolean to be the default in tests. This makes === consistent between tests and production code.

Throws TestCanceledException to indicate a test was canceled.

Throws TestCanceledException, with the passed String message as the exception's detail message, to indicate a test was canceled.

Throws TestCanceledException, with the passed String message as the exception's detail message and Throwable cause, to indicate a test failed.

Throws TestCanceledException, with the passed Throwable cause, to indicate a test failed. The getMessage method of the thrown TestCanceledException will return cause.toString.

Throws TestFailedException to indicate a test failed.

Throws TestFailedException, with the passed String message as the exception's detail message, to indicate a test failed.

Throws TestFailedException, with the passed String message as the exception's detail message and Throwable cause, to indicate a test failed.

Throws TestFailedException, with the passed Throwable cause, to indicate a test failed. The getMessage method of the thrown TestFailedException will return cause.toString.

Intercept and return an exception that's expected to be thrown by the passed function value. The thrown exception must be an instance of the type specified by the type parameter of this method. This method invokes the passed function. If the function throws an exception that's an instance of the specified type, this method returns that exception. Else, whether the passed function returns normally or completes abruptly with a different exception, this method throws TestFailedException.

Note that the type specified as this method's type parameter may represent any subtype of AnyRef, not just Throwable or one of its subclasses. In Scala, exceptions can be caught based on traits they implement, so it may at times make sense to specify a trait that the intercepted exception's class must mix in. If a class instance is passed for a type that could not possibly be used to catch an exception (such as String, for example), this method will complete abruptly with a TestFailedException.

Also note that the difference between this method and assertThrows is that this method returns the expected exception, so it lets you perform further assertions on that exception. By contrast, the assertThrows method returns Succeeded, which means it can serve as the last statement in an async- or safe-style suite. assertThrows also indicates to the reader of the code that nothing further is expected about the thrown exception other than its type. The recommended usage is to use assertThrows by default, intercept only when you need to inspect the caught exception further.

Throws TestPendingException to indicate a test is pending.

A pending test is one that has been given a name but is not yet implemented. The purpose of pending tests is to facilitate a style of testing in which documentation of behavior is sketched out before tests are written to verify that behavior (and often, the before the behavior of the system being tested is itself implemented). Such sketches form a kind of specification of what tests and functionality to implement later.

To support this style of testing, a test can be given a name that specifies one bit of behavior required by the system being tested. The test can also include some code that sends more information about the behavior to the reporter when the tests run. At the end of the test, it can call method pending, which will cause it to complete abruptly with TestPendingException. Because tests in ScalaTest can be designated as pending with TestPendingException, both the test name and any information sent to the reporter when running the test can appear in the report of a test run. (In other words, the code of a pending test is executed just like any other test.) However, because the test completes abruptly with TestPendingException, the test will be reported as pending, to indicate the actual test, and possibly the functionality it is intended to test, has not yet been implemented.

Note: This method always completes abruptly with a TestPendingException. Thus it always has a side effect. Methods with side effects are usually invoked with parentheses, as in pending(). This method is defined as a parameterless method, in flagrant contradiction to recommended Scala style, because it forms a kind of DSL for pending tests. It enables tests in suites such as FunSuite or FunSpec to be denoted by placing "(pending)" after the test name, as in:

test("that style rules are not laws") (pending)

Readers of the code see "pending" in parentheses, which looks like a little note attached to the test name to indicate it is pending. Whereas "(pending()) looks more like a method call, "(pending)" lets readers stay at a higher level, forgetting how it is implemented and just focusing on the intent of the programmer who wrote the code.

Execute the passed block of code, and if it completes abruptly, throw TestPendingException, else throw TestFailedException.

This method can be used to temporarily change a failing test into a pending test in such a way that it will automatically turn back into a failing test once the problem originally causing the test to fail has been fixed. At that point, you need only remove the pendingUntilFixed call. In other words, a pendingUntilFixed surrounding a block of code that isn't broken is treated as a test failure. The motivation for this behavior is to encourage people to remove pendingUntilFixed calls when there are no longer needed.

This method facilitates a style of testing in which tests are written before the code they test. Sometimes you may encounter a test failure that requires more functionality than you want to tackle without writing more tests. In this case you can mark the bit of test code causing the failure with pendingUntilFixed. You can then write more tests and functionality that eventually will get your production code to a point where the original test won't fail anymore. At this point the code block marked with pendingUntilFixed will no longer throw an exception (because the problem has been fixed). This will in turn cause pendingUntilFixed to throw TestFailedException with a detail message explaining you need to go back and remove the pendingUntilFixed call as the problem orginally causing your test code to fail has been fixed.

Executes the block of code passed as the second parameter, and, if it completes abruptly with a ModifiableMessage exception, prepends the "clue" string passed as the first parameter to the beginning of the detail message of that thrown exception, then rethrows it. If clue does not end in a white space character, one space will be added between it and the existing detail message (unless the detail message is not defined).

This method allows you to add more information about what went wrong that will be reported when a test fails. Here's an example:

withClue("(Employee's name was: " + employee.name + ")") {
 intercept[IllegalArgumentException] {
   employee.getTask(-1)
 }
}

If an invocation of intercept completed abruptly with an exception, the resulting message would be something like:

(Employee's name was Bob Jones) Expected IllegalArgumentException to be thrown, but no exception was thrown

Trap and return any thrown exception that would normally cause a ScalaTest test to fail, or create and return a new RuntimeException indicating no exception is thrown.

This method is intended to be used in the Scala interpreter to eliminate large stack traces when trying out ScalaTest assertions and matcher expressions. It is not intended to be used in regular test code. If you want to ensure that a bit of code throws an expected exception, use intercept, not trap. Here's an example interpreter session without trap:

scala> import org.scalatest._
import org.scalatest._

scala> import Matchers._
import Matchers._

scala> val x = 12
a: Int = 12

scala> x shouldEqual 13
org.scalatest.exceptions.TestFailedException: 12 did not equal 13
  at org.scalatest.Assertions$class.newAssertionFailedException(Assertions.scala:449)
  at org.scalatest.Assertions$.newAssertionFailedException(Assertions.scala:1203)
  at org.scalatest.Assertions$AssertionsHelper.macroAssertTrue(Assertions.scala:417)
  at .<init>(<console>:15)
  at .<clinit>(<console>)
  at .<init>(<console>:7)
  at .<clinit>(<console>)
  at $print(<console>)
  at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
  at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
  at java.lang.reflect.Method.invoke(Method.java:597)
  at scala.tools.nsc.interpreter.IMain$ReadEvalPrint.call(IMain.scala:731)
  at scala.tools.nsc.interpreter.IMain$Request.loadAndRun(IMain.scala:980)
  at scala.tools.nsc.interpreter.IMain.loadAndRunReq$1(IMain.scala:570)
  at scala.tools.nsc.interpreter.IMain.interpret(IMain.scala:601)
  at scala.tools.nsc.interpreter.IMain.interpret(IMain.scala:565)
  at scala.tools.nsc.interpreter.ILoop.reallyInterpret$1(ILoop.scala:745)
  at scala.tools.nsc.interpreter.ILoop.interpretStartingWith(ILoop.scala:790)
  at scala.tools.nsc.interpreter.ILoop.command(ILoop.scala:702)
  at scala.tools.nsc.interpreter.ILoop.processLine$1(ILoop.scala:566)
  at scala.tools.nsc.interpreter.ILoop.innerLoop$1(ILoop.scala:573)
  at scala.tools.nsc.interpreter.ILoop.loop(ILoop.scala:576)
  at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply$mcZ$sp(ILoop.scala:867)
  at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply(ILoop.scala:822)
  at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply(ILoop.scala:822)
  at scala.tools.nsc.util.ScalaClassLoader$.savingContextLoader(ScalaClassLoader.scala:135)
  at scala.tools.nsc.interpreter.ILoop.process(ILoop.scala:822)
  at scala.tools.nsc.MainGenericRunner.runTarget$1(MainGenericRunner.scala:83)
  at scala.tools.nsc.MainGenericRunner.process(MainGenericRunner.scala:96)
  at scala.tools.nsc.MainGenericRunner$.main(MainGenericRunner.scala:105)
  at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)

That's a pretty tall stack trace. Here's what it looks like when you use trap:

scala> trap { x shouldEqual 13 }
res1: Throwable = org.scalatest.exceptions.TestFailedException: 12 did not equal 13

Much less clutter. Bear in mind, however, that if no exception is thrown by the passed block of code, the trap method will create a new NormalResult (a subclass of Throwable made for this purpose only) and return that. If the result was the Unit value, it will simply say that no exception was thrown:

scala> trap { x shouldEqual 12 }
res2: Throwable = No exception was thrown.

If the passed block of code results in a value other than Unit, the NormalResult's toString will print the value:

scala> trap { "Dude!" }
res3: Throwable = No exception was thrown. Instead, result was: "Dude!"

Although you can access the result value from the NormalResult, its type is Any and therefore not very convenient to use. It is not intended that trap be used in test code. The sole intended use case for trap is decluttering Scala interpreter sessions by eliminating stack traces when executing assertion and matcher expressions.

Returns a TripleEqualsInvocationOnSpread[T], given an Spread[T], to facilitate the “<left> should !== (<pivot> +- <tolerance>)” syntax of Matchers.

Returns a TripleEqualsInvocation[Null], given a null reference, to facilitate the “<left> should !== null” syntax of Matchers.

Returns a TripleEqualsInvocation[T], given an object of type T, to facilitate the “<left> should !== <right>” syntax of Matchers.

Returns a TripleEqualsInvocationOnSpread[T], given an Spread[T], to facilitate the “<left> should === (<pivot> +- <tolerance>)” syntax of Matchers.

Returns a TripleEqualsInvocation[Null], given a null reference, to facilitate the “<left> should === null” syntax of Matchers.

Returns a TripleEqualsInvocation[T], given an object of type T, to facilitate the “<left> should === <right>” syntax of Matchers.

Returns an Equality[A] for any type A that determines equality by first calling .deep on any Array (on either the left or right side), then comparing the resulting objects with ==.

The Succeeded singleton.

You can use succeed to solve a type error when an async test does not end in either Future[Assertion] or Assertion. Because Assertion is a type alias for Succeeded.type, putting succeed at the end of a test body (or at the end of a function being used to map the final future of a test body) will solve the type error.