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 
21 import java.util.Collections;
22 import 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  * <p>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  * @author Kevin Bourrillion
61  * @author Chris Povirk
62  */
63 @GwtCompatible
64 public abstract class IteratorTester<E> extends
65     AbstractIteratorTester<E, Iterator<E>> {
66   /**
67    * Creates an IteratorTester.
68    *
69    * @param steps how many operations to test for each tested pair of iterators
70    * @param features the features supported by the iterator
71    */
IteratorTester(int steps, Iterable<? extends IteratorFeature> features, Iterable<E> expectedElements, KnownOrder knownOrder)72   protected IteratorTester(int steps,
73       Iterable<? extends IteratorFeature> features,
74       Iterable<E> expectedElements, KnownOrder knownOrder) {
75     super(steps, Collections.<E>singleton(null), features, expectedElements,
76         knownOrder, 0);
77   }
78 
79   @Override
getStimulusValues()80   protected final Iterable<Stimulus<E, Iterator<E>>> getStimulusValues() {
81     return iteratorStimuli();
82   }
83 }
84