IteratorTester.java revision dbd967a6e5c96cc1a97c5521f88dc1564ba2f81b 
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 java.util.Collections;
20import java.util.Iterator;
21
22/**
23 * A utility for testing an Iterator implementation by comparing its behavior to
24 * that of a "known good" reference implementation. In order to accomplish this,
25 * it's important to test a great variety of sequences of the
26 * {@link Iterator#next}, {@link Iterator#hasNext} and {@link Iterator#remove}
27 * operations. This utility takes the brute-force approach of trying <i>all</i>
28 * possible sequences of these operations, up to a given number of steps. So, if
29 * the caller specifies to use <i>n</i> steps, a total of <i>3^n</i> tests are
30 * actually performed.
31 *
32 * <p>For instance, if <i>steps</i> is 5, one example sequence that will be
33 * tested is:
34 *
35 * <ol>
36 * <li>remove();
37 * <li>hasNext()
38 * <li>hasNext();
39 * <li>remove();
40 * <li>next();
41 * </ol>
42 *
43 * This particular order of operations may be unrealistic, and testing all 3^5
44 * of them may be thought of as overkill; however, it's difficult to determine
45 * which proper subset of this massive set would be sufficient to expose any
46 * possible bug. Brute force is simpler.
47 *
48 * <p>To use this class the concrete subclass must implement the
49 * {@link IteratorTester#newTargetIterator()} method. This is because it's
50 * impossible to test an Iterator without changing its state, so the tester
51 * needs a steady supply of fresh Iterators.
52 *
53 * <p>If your iterator supports modification through {@code remove()}, you may
54 * wish to override the verify() method, which is called <em>after</em>
55 * each sequence and is guaranteed to be called using the latest values
56 * obtained from {@link IteratorTester#newTargetIterator()}.
57 *
58 * <p>This class is GWT compatible.
59 *
60 * @author Kevin Bourrillion
61 * @author Chris Povirk
62 */
63public abstract class IteratorTester<E> extends
64    AbstractIteratorTester<E, Iterator<E>> {
65  /**
66   * Creates an IteratorTester.
67   *
68   * @param steps how many operations to test for each tested pair of iterators
69   * @param features the features supported by the iterator
70   */
71  protected IteratorTester(int steps,
72      Iterable<? extends IteratorFeature> features,
73      Iterable<E> expectedElements, KnownOrder knownOrder) {
74    super(steps, Collections.<E>singleton(null), features, expectedElements,
75        knownOrder, 0);
76  }
77
78  @Override
79  protected final Iterable<Stimulus<E, Iterator<E>>> getStimulusValues() {
80    return iteratorStimuli();
81  }
82}
83