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
17 package com.google.common.collect.testing;
18
19 import com.google.common.annotations.GwtCompatible;
20 import java.util.Collections;
21 import java.util.Iterator;
22
23 /**
24 * A utility for testing an Iterator implementation by comparing its behavior to that of a "known
25 * good" reference implementation. In order to accomplish this, it's important to test a great
26 * variety of sequences of the {@link Iterator#next}, {@link Iterator#hasNext} and {@link
27 * Iterator#remove} 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 the caller
29 * specifies to use <i>n</i> steps, a total of <i>3^n</i> tests are actually performed.
30 *
31 * <p>For instance, if <i>steps</i> is 5, one example sequence that will be tested is:
32 *
33 * <ol>
34 * <li>remove();
35 * <li>hasNext()
36 * <li>hasNext();
37 * <li>remove();
38 * <li>next();
39 * </ol>
40 *
41 * <p>This particular order of operations may be unrealistic, and testing all 3^5 of them may be
42 * thought of as overkill; however, it's difficult to determine which proper subset of this massive
43 * set would be sufficient to expose any possible bug. Brute force is simpler.
44 *
45 * <p>To use this class the concrete subclass must implement the {@link
46 * IteratorTester#newTargetIterator()} method. This is because it's impossible to test an Iterator
47 * without changing its state, so the tester needs a steady supply of fresh Iterators.
48 *
49 * <p>If your iterator supports modification through {@code remove()}, you may wish to override the
50 * verify() method, which is called <em>after</em> each sequence and is guaranteed to be called
51 * using the latest values obtained from {@link IteratorTester#newTargetIterator()}.
52 *
53 * <p>The value you pass to the parameter {@code steps} should be greater than the length of your
54 * iterator, so that this class can check that your iterator behaves correctly when it is exhausted.
55 *
56 * <p>For example, to test {@link java.util.Collections#unmodifiableList(java.util.List)
57 * Collections.unmodifiableList}'s iterator:
58 *
59 * <pre>{@code
60 * List<String> expectedElements =
61 * Arrays.asList("a", "b", "c", "d", "e");
62 * List<String> actualElements =
63 * Collections.unmodifiableList(
64 * Arrays.asList("a", "b", "c", "d", "e"));
65 * IteratorTester<String> iteratorTester =
66 * new IteratorTester<String>(
67 * 6,
68 * IteratorFeature.UNMODIFIABLE,
69 * expectedElements,
70 * IteratorTester.KnownOrder.KNOWN_ORDER) {
71 * @Override
72 * protected Iterator<String> newTargetIterator() {
73 * return actualElements.iterator();
74 * }
75 * };
76 * iteratorTester.test();
77 * iteratorTester.testForEachRemaining();
78 * }</pre>
79 *
80 * <p><b>Note</b>: It is necessary to use {@code IteratorTester.KnownOrder} as shown above, rather
81 * than {@code KnownOrder} directly, because otherwise the code cannot be compiled.
82 *
83 * @author Kevin Bourrillion
84 * @author Chris Povirk
85 */
86 @GwtCompatible
87 public abstract class IteratorTester<E> extends AbstractIteratorTester<E, Iterator<E>> {
88 /**
89 * Creates an IteratorTester.
90 *
91 * @param steps how many operations to test for each tested pair of iterators
92 * @param features the features supported by the iterator
93 */
94 protected IteratorTester(
95 int steps,
96 Iterable<? extends IteratorFeature> features,
97 Iterable<E> expectedElements,
98 KnownOrder knownOrder) {
99 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 }