sizesToTest.retainAll(features);
    features.removeAll(sizesToTest);

    addImpliedFeatures(sizesToTest);
    sizesToTest.retainAll(asList(CollectionSize.ZERO, CollectionSize.ONE, CollectionSize.SEVERAL));

    logger.fine("   Sizes: " + formatFeatureSet(sizesToTest));

    if (sizesToTest.isEmpty()) {
      throw new IllegalStateException(
          name

    Collection<Entry<K, V>> entries = getSampleEntries(getNumEntries() - 1);
    entries.add(entry(null, v3()));
    Map<K, V> other = newHashMap(entries);

    assertFalse(
        "Two Maps should not be equal if exactly one of them contains a null key.",
        getMap().equals(other));
  }

  @CollectionSize.Require(absent = CollectionSize.ZERO)
  @MapFeature.Require(ALLOWS_NULL_VALUES)
  public void testEquals_containingNullValue() {

    int initialSize = getMap().size();
    assertEquals("remove(present) should return the associated value", v0(), getMap().remove(k0()));
    assertEquals(
        "remove(present) should decrease a map's size by one.", initialSize - 1, getMap().size());
    expectMissing(e0());
  }

  @MapFeature.Require({FAILS_FAST_ON_CONCURRENT_MODIFICATION, SUPPORTS_REMOVE})
  @CollectionSize.Require(SEVERAL)

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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
 *

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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
 *

  private double sumOfProductsOfDeltas = 0.0;

  /** Adds the given pair of values to the dataset. */
  public void add(double x, double y) {
    // We extend the recursive expression for the one-variable case at Art of Computer Programming
    // vol. 2, Knuth, 4.2.2, (16) to the two-variable case. We have two value series x_i and y_i.

import static com.google.common.collect.testing.Helpers.mapEntry;
import static com.google.common.collect.testing.features.CollectionFeature.SUPPORTS_ITERATOR_REMOVE;
import static com.google.common.collect.testing.features.CollectionSize.ONE;
import static com.google.common.collect.testing.features.CollectionSize.SEVERAL;
import static com.google.common.collect.testing.features.CollectionSize.ZERO;

   * probably work around it by changing how we annotate the J2CL EnumMap, but that's probably more
   * trouble than just using Object.class.)
   *
   * Then we declare the getters for these fields as @GwtIncompatible so that no one can try to use
   * them under J2CL—or, as an unfortunate side effect, under GWT. We do still give the fields
   * themselves their proper values under GWT, since GWT's EnumMap does need the Class instance.
   *

import static com.google.common.collect.testing.Helpers.mapEntry;
import static com.google.common.collect.testing.features.CollectionFeature.SUPPORTS_ITERATOR_REMOVE;
import static com.google.common.collect.testing.features.CollectionSize.ONE;
import static com.google.common.collect.testing.features.CollectionSize.SEVERAL;
import static com.google.common.collect.testing.features.CollectionSize.ZERO;

   * probably work around it by changing how we annotate the J2CL EnumMap, but that's probably more
   * trouble than just using Object.class.)
   *
   * Then we declare the getters for these fields as @GwtIncompatible so that no one can try to use
   * them under J2CL—or, as an unfortunate side effect, under GWT. We do still give the fields
   * themselves their proper values under GWT, since GWT's EnumMap does need the Class instance.
   *