e, obj + " must not be Object#equals to an arbitrary object of another class");
      return;
    }
    fail("Should get equal to incompatible class error");
  }

  /** Test proper handling where an object is not equal to one the user has said should be equal */
  public void testInvalidNotEqualsEqualObject() {
    equalsTester.addEqualityGroup(reference, notEqualObject1);
    try {

   * A specification for which index to return if the list contains at least one element that
   * compares as equal to the key.
   */
  enum KeyPresentBehavior {
    /**
     * Return the index of any list element that compares as equal to the key. No guarantees are
     * made as to which index is returned, if more than one element compares as equal to the key.
     */
    ANY_PRESENT {
      @Override

    /** Returns the value from the right map (possibly null). */
    @ParametricNullness
    V rightValue();

    /**
     * Two instances are considered equal if their {@link #leftValue()} values are equal and their
     * {@link #rightValue()} values are also equal.
     */
    @Override
    boolean equals(@Nullable Object other);

    /**

    /**
     * Do not instantiate.
     */
    protected ObjectUtil() {
    }

    /**
     * Returns true if the two objects are equal, or both are null.
     *
     * @param object1 the first object
     * @param object2 the second object
     * @return true if equal or both null, false otherwise
     */
    public static boolean equals(final Object object1, final Object object2) {
        if (object1 == object2) {

 *   <li>comparing each pair of objects within the same equality group returns true
 *   <li>comparing each pair of objects from different equality groups returns false
 *   <li>the hash codes of any two equal objects are equal
 * </ul>
 *
 * <p>When a test fails, the error message labels the objects involved in the failed comparison as
 * follows:
 *
 * <ul>

        assertFalse(r1.hashCode() == r3.hashCode());

        assertTrue(r1.equals(r2), "Expected " + r1 + " to equal " + r2);
        assertTrue(r2.equals(r1), "Expected " + r2 + " to equal " + r1);

        assertFalse(r1.equals(r3), "Expected " + r1 + " to not equal " + r3);
        assertFalse(r3.equals(r1), "Expected " + r3 + " to not equal " + r1);
    }

   * A specification for which index to return if the list contains at least one element that
   * compares as equal to the key.
   */
  enum KeyPresentBehavior {
    /**
     * Return the index of any list element that compares as equal to the key. No guarantees are
     * made as to which index is returned, if more than one element compares as equal to the key.
     */
    ANY_PRESENT {
      @Override

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

  @CollectionSize.Require(absent = CollectionSize.ZERO)
  public void testEquals_smallerMap() {
    Collection<Entry<K, V>> fewerEntries = getSampleEntries(getNumEntries() - 1);
    assertFalse(
        "Maps of different sizes should not be equal.", getMap().equals(newHashMap(fewerEntries)));
  }

    assertTrue("An Object should be equal to itself.", collection.equals(collection));
  }

  // Comparisons to null *are* defined.
  @SuppressWarnings("UndefinedEquals")
  public void testEquals_null() {
    // noinspection ObjectEqualsNull
    assertFalse("An object should not be equal to null.", collection.equals(null));
  }

  // A collection should essentially never be equal to a non-collection.

     * Implementations must ensure that if two requests are equal according to
     * {@link #equals(Object)}, they have the same hashcode.
     *
     * @return a hash code value for this request
     */
    @Override
    int hashCode();

    /**
     * Returns {@code true} if the specified object is equal to this request.
     * Two requests are considered equal if they have the same type and all
     * significant fields are equal.