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/*
* Copyright (C) 2007 The Guava Authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.common.collect.testing;
import com.google.common.annotations.GwtCompatible;
import java.util.Collections;
import java.util.Iterator;
import org.checkerframework.checker.nullness.qual.Nullable;
/**
* A utility for testing an Iterator implementation by comparing its behavior to that of a "known
* good" reference implementation. In order to accomplish this, it's important to test a great
* variety of sequences of the {@link Iterator#next}, {@link Iterator#hasNext} and {@link
* Iterator#remove} operations. This utility takes the brute-force approach of trying all
* possible sequences of these operations, up to a given number of steps. So, if the caller
* specifies to use n steps, a total of 3^n tests are actually performed.
*
* For instance, if steps is 5, one example sequence that will be tested is:
*
*
* - remove();
*
- hasNext()
*
- hasNext();
*
- remove();
*
- next();
*
*
* This particular order of operations may be unrealistic, and testing all 3^5 of them may be
* thought of as overkill; however, it's difficult to determine which proper subset of this massive
* set would be sufficient to expose any possible bug. Brute force is simpler.
*
*
To use this class the concrete subclass must implement the {@link
* IteratorTester#newTargetIterator()} method. This is because it's impossible to test an Iterator
* without changing its state, so the tester needs a steady supply of fresh Iterators.
*
*
If your iterator supports modification through {@code remove()}, you may wish to override the
* verify() method, which is called after each sequence and is guaranteed to be called
* using the latest values obtained from {@link IteratorTester#newTargetIterator()}.
*
*
The value you pass to the parameter {@code steps} should be greater than the length of your
* iterator, so that this class can check that your iterator behaves correctly when it is exhausted.
*
*
For example, to test {@link java.util.Collections#unmodifiableList(java.util.List)
* Collections.unmodifiableList}'s iterator:
*
*
{@code
* List expectedElements =
* Arrays.asList("a", "b", "c", "d", "e");
* List actualElements =
* Collections.unmodifiableList(
* Arrays.asList("a", "b", "c", "d", "e"));
* IteratorTester iteratorTester =
* new IteratorTester(
* 6,
* IteratorFeature.UNMODIFIABLE,
* expectedElements,
* IteratorTester.KnownOrder.KNOWN_ORDER) {
* @Override
* protected Iterator newTargetIterator() {
* return actualElements.iterator();
* }
* };
* iteratorTester.test();
* iteratorTester.testForEachRemaining();
* }
*
* Note: It is necessary to use {@code IteratorTester.KnownOrder} as shown above, rather
* than {@code KnownOrder} directly, because otherwise the code cannot be compiled.
*
* @author Kevin Bourrillion
* @author Chris Povirk
*/
@GwtCompatible
@ElementTypesAreNonnullByDefault
public abstract class IteratorTester
extends AbstractIteratorTester> {
/**
* Creates an IteratorTester.
*
* @param steps how many operations to test for each tested pair of iterators
* @param features the features supported by the iterator
*/
protected IteratorTester(
int steps,
Iterable features,
Iterable expectedElements,
KnownOrder knownOrder) {
super(steps, Collections.singleton(null), features, expectedElements, knownOrder, 0);
}
@Override
protected final Iterable>> getStimulusValues() {
return iteratorStimuli();
}
}