001/*
002 * Copyright (C) 2007 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package com.google.common.collect.testing;
018
019import com.google.common.annotations.GwtCompatible;
020import java.util.Collections;
021import java.util.Iterator;
022
023/**
024 * A utility for testing an Iterator implementation by comparing its behavior to that of a "known
025 * good" reference implementation. In order to accomplish this, it's important to test a great
026 * variety of sequences of the {@link Iterator#next}, {@link Iterator#hasNext} and {@link
027 * Iterator#remove} operations. This utility takes the brute-force approach of trying <i>all</i>
028 * possible sequences of these operations, up to a given number of steps. So, if the caller
029 * specifies to use <i>n</i> steps, a total of <i>3^n</i> tests are actually performed.
030 *
031 * <p>For instance, if <i>steps</i> is 5, one example sequence that will be tested is:
032 *
033 * <ol>
034 *   <li>remove();
035 *   <li>hasNext()
036 *   <li>hasNext();
037 *   <li>remove();
038 *   <li>next();
039 * </ol>
040 *
041 * <p>This particular order of operations may be unrealistic, and testing all 3^5 of them may be
042 * thought of as overkill; however, it's difficult to determine which proper subset of this massive
043 * set would be sufficient to expose any possible bug. Brute force is simpler.
044 *
045 * <p>To use this class the concrete subclass must implement the {@link
046 * IteratorTester#newTargetIterator()} method. This is because it's impossible to test an Iterator
047 * without changing its state, so the tester needs a steady supply of fresh Iterators.
048 *
049 * <p>If your iterator supports modification through {@code remove()}, you may wish to override the
050 * verify() method, which is called <em>after</em> each sequence and is guaranteed to be called
051 * using the latest values obtained from {@link IteratorTester#newTargetIterator()}.
052 *
053 * <p>The value you pass to the parameter {@code steps} should be greater than the length of your
054 * iterator, so that this class can check that your iterator behaves correctly when it is exhausted.
055 *
056 * <p>For example, to test {@link java.util.Collections#unmodifiableList(java.util.List)
057 * Collections.unmodifiableList}'s iterator:
058 *
059 * <pre>{@code
060 * List<String> expectedElements =
061 *     Arrays.asList("a", "b", "c", "d", "e");
062 * List<String> actualElements =
063 *     Collections.unmodifiableList(
064 *         Arrays.asList("a", "b", "c", "d", "e"));
065 * IteratorTester<String> iteratorTester =
066 *     new IteratorTester<String>(
067 *         6,
068 *         IteratorFeature.UNMODIFIABLE,
069 *         expectedElements,
070 *         IteratorTester.KnownOrder.KNOWN_ORDER) {
071 *       @Override
072 *       protected Iterator<String> newTargetIterator() {
073 *         return actualElements.iterator();
074 *       }
075 *     };
076 * iteratorTester.test();
077 * iteratorTester.testForEachRemaining();
078 * }</pre>
079 *
080 * <p><b>Note</b>: It is necessary to use {@code IteratorTester.KnownOrder} as shown above, rather
081 * than {@code KnownOrder} directly, because otherwise the code cannot be compiled.
082 *
083 * @author Kevin Bourrillion
084 * @author Chris Povirk
085 */
086@GwtCompatible
087public abstract class IteratorTester<E> extends AbstractIteratorTester<E, Iterator<E>> {
088  /**
089   * Creates an IteratorTester.
090   *
091   * @param steps how many operations to test for each tested pair of iterators
092   * @param features the features supported by the iterator
093   */
094  protected IteratorTester(
095      int steps,
096      Iterable<? extends IteratorFeature> features,
097      Iterable<E> expectedElements,
098      KnownOrder knownOrder) {
099    super(steps, Collections.<E>singleton(null), features, expectedElements, knownOrder, 0);
100  }
101
102  @Override
103  protected final Iterable<Stimulus<E, Iterator<E>>> getStimulusValues() {
104    return iteratorStimuli();
105  }
106}