}

  @Retention(RetentionPolicy.RUNTIME)
  @Inherited
  @TesterAnnotation
  public @interface Require {
    public abstract SetFeature[] value() default {};

    public abstract SetFeature[] absent() default {};
  }

  }

  @Retention(RetentionPolicy.RUNTIME)
  @Inherited
  @TesterAnnotation
  public @interface Require {
    public abstract SetFeature[] value() default {};

    public abstract SetFeature[] absent() default {};
  }

    And this path operation will:

    * Send the invoice to the client.
    * Collect the money from the client.
    * Send a notification back to the API user (the external developer), as a callback.
        * At this point is that the API will somehow send a POST request to the
            external API with the notification of the invoice event
            (e.g. "payment successful").
    """

@SuppressWarnings("JUnit4ClassUsedInJUnit3")
public class ListRemoveTester<E> extends AbstractListTester<E> {
  @CollectionFeature.Require(SUPPORTS_REMOVE)
  @CollectionSize.Require(absent = {ZERO, ONE})
  public void testRemove_duplicate() {
    ArrayWithDuplicate<E> arrayAndDuplicate = createArrayWithDuplicateElement();
    collection = getSubjectGenerator().create(arrayAndDuplicate.elements);

@ElementTypesAreNonnullByDefault
public interface RemovalListener<K, V> {
  /**
   * Notifies the listener that a removal occurred at some point in the past.
   *
   * <p>This does not always signify that the key is now absent from the cache, as it may have
   * already been re-added.
   */
  // Technically should accept RemovalNotification<? extends K, ? extends V>, but because

    return implied;
  }

  @Retention(RetentionPolicy.RUNTIME)
  @Inherited
  @TesterAnnotation
  public @interface Require {
    ListFeature[] value() default {};

    ListFeature[] absent() default {};
  }

  }

  @Retention(RetentionPolicy.RUNTIME)
  @Inherited
  @TesterAnnotation
  public @interface Require {
    public abstract MultimapFeature[] value() default {};

    public abstract MultimapFeature[] absent() default {};
  }

@SuppressWarnings("JUnit4ClassUsedInJUnit3")
public class SetRemoveTester<E> extends AbstractSetTester<E> {
  @CollectionFeature.Require(SUPPORTS_REMOVE)
  @CollectionSize.Require(absent = ZERO)
  public void testRemove_present() {
    getSet().remove(e0());
    assertFalse(
        "After remove(present) a set should not contain the removed element.",
        getSet().contains(e0()));
  }

@SuppressWarnings("JUnit4ClassUsedInJUnit3")
public class SetRemoveTester<E> extends AbstractSetTester<E> {
  @CollectionFeature.Require(SUPPORTS_REMOVE)
  @CollectionSize.Require(absent = ZERO)
  public void testRemove_present() {
    getSet().remove(e0());
    assertFalse(
        "After remove(present) a set should not contain the removed element.",
        getSet().contains(e0()));
  }

   * opening the data stream.
   *
   * <p>The default implementation returns {@link Optional#absent}. Some sources, such as a {@code
   * CharSequence}, may return a non-absent value. Note that in such cases, it is <i>possible</i>
   * that this method will return a different number of chars than would be returned by reading all
   * of the chars.
   *