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Guava testlib is a set of java classes used for more convenient unit testing - particularly to assist the tests for Guava itself.

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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;

/**
 * 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()}.
 *
 * @author Kevin Bourrillion
 * @author Chris Povirk
 */
@GwtCompatible
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();
  }
}