xref: /external/guava/guava-testlib/src/com/google/common/collect/testing/IteratorTester.java

/*
 * 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 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 <i>all</i>
 * possible sequences of these operations, up to a given number of steps. So, if
 * the caller specifies to use <i>n</i> steps, a total of <i>3^n</i> tests are
 * actually performed.
 *
 * <p>For instance, if <i>steps</i> is 5, one example sequence that will be
 * tested is:
 *
 * <ol>
 * <li>remove();
 * <li>hasNext()
 * <li>hasNext();
 * <li>remove();
 * <li>next();
 * </ol>
 *
 * 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.
 *
 * <p>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.
 *
 * <p>If your iterator supports modification through {@code remove()}, you may
 * wish to override the verify() method, which is called <em>after</em>
 * each sequence and is guaranteed to be called using the latest values
 * obtained from {@link IteratorTester#newTargetIterator()}.
 *
 * <p>This class is GWT compatible.
 *
 * @author Kevin Bourrillion
 * @author Chris Povirk
 */
public abstract class IteratorTester<E> extends
    AbstractIteratorTester<E, Iterator<E>> {
  /**
   * 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<? extends IteratorFeature> features,
      Iterable<E> expectedElements, KnownOrder knownOrder) {
    super(steps, Collections.<E>singleton(null), features, expectedElements,
        knownOrder, 0);
  }

  @Override
  protected final Iterable<Stimulus<E, Iterator<E>>> getStimulusValues() {
    return iteratorStimuli();
  }
}