IteratorTester.java revision 3c77433663281544363151bf284b0240dfd22a42 
1/*
2 * Copyright (C) 2007 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.google.common.collect.testing;
18
19import com.google.common.annotations.GwtCompatible;
20
21import java.util.Collections;
22import java.util.Iterator;
23
24/**
25 * A utility for testing an Iterator implementation by comparing its behavior to
26 * that of a "known good" reference implementation. In order to accomplish this,
27 * it's important to test a great variety of sequences of the
28 * {@link Iterator#next}, {@link Iterator#hasNext} and {@link Iterator#remove}
29 * operations. This utility takes the brute-force approach of trying <i>all</i>
30 * possible sequences of these operations, up to a given number of steps. So, if
31 * the caller specifies to use <i>n</i> steps, a total of <i>3^n</i> tests are
32 * actually performed.
33 *
34 * <p>For instance, if <i>steps</i> is 5, one example sequence that will be
35 * tested is:
36 *
37 * <ol>
38 * <li>remove();
39 * <li>hasNext()
40 * <li>hasNext();
41 * <li>remove();
42 * <li>next();
43 * </ol>
44 *
45 * This particular order of operations may be unrealistic, and testing all 3^5
46 * of them may be thought of as overkill; however, it's difficult to determine
47 * which proper subset of this massive set would be sufficient to expose any
48 * possible bug. Brute force is simpler.
49 *
50 * <p>To use this class the concrete subclass must implement the
51 * {@link IteratorTester#newTargetIterator()} method. This is because it's
52 * impossible to test an Iterator without changing its state, so the tester
53 * needs a steady supply of fresh Iterators.
54 *
55 * <p>If your iterator supports modification through {@code remove()}, you may
56 * wish to override the verify() method, which is called <em>after</em>
57 * each sequence and is guaranteed to be called using the latest values
58 * obtained from {@link IteratorTester#newTargetIterator()}.
59 *
60 * <p>This class is GWT compatible.
61 *
62 * @author Kevin Bourrillion
63 * @author Chris Povirk
64 */
65@GwtCompatible
66public abstract class IteratorTester<E> extends
67    AbstractIteratorTester<E, Iterator<E>> {
68  /**
69   * Creates an IteratorTester.
70   *
71   * @param steps how many operations to test for each tested pair of iterators
72   * @param features the features supported by the iterator
73   */
74  protected IteratorTester(int steps,
75      Iterable<? extends IteratorFeature> features,
76      Iterable<E> expectedElements, KnownOrder knownOrder) {
77    super(steps, Collections.<E>singleton(null), features, expectedElements,
78        knownOrder, 0);
79  }
80
81  @Override
82  protected final Iterable<Stimulus<E, Iterator<E>>> getStimulusValues() {
83    return iteratorStimuli();
84  }
85}
86