String getSource();

    /**
     * Gets the one-based index of the line containing the problem. The line number should refer to some text file that
     * is given by {@link #getSource()}.
     *
     * @return the one-based index of the line containing the problem or a non-positive value if unknown
     */
    int getLineNumber();

    /**

    /**
     * If the module path contains at least one filename-based auto-module, prepares a warning message.
     * The module path is the collection of dependencies associated with {@link JavaPathType#MODULES}.
     * It is caller's responsibility to send the message to a logger.
     *
     * @return warning message if at least one filename-based auto-module was found
     */

  /** Test an empty collection. */
  ZERO(0),
  /** Test a one-element collection. */
  ONE(1),
  /** Test a three-element collection. */
  SEVERAL(3),
  /*
   * TODO: add VERY_LARGE, noting that we currently assume that the fourth
   * sample element is not in any collection
   */

  ANY(ZERO, ONE, SEVERAL);

  private final Set<Feature<? super Collection>> implied;

  /** Test an empty collection. */
  ZERO(0),
  /** Test a one-element collection. */
  ONE(1),
  /** Test a three-element collection. */
  SEVERAL(3),
  /*
   * TODO: add VERY_LARGE, noting that we currently assume that the fourth
   * sample element is not in any collection
   */

  ANY(ZERO, ONE, SEVERAL);

  private final Set<Feature<? super Collection>> implied;

growing, and very soon had to kneel down on the floor:  in
another minute there was not even room for this, and she tried
the effect of lying down with one elbow against the door, and the
other arm curled round her head.  Still she went on growing, and,
as a last resource, she put one arm out of the window, and one
foot up the chimney, and said to herself `Now I can do no more,
whatever happens.  What WILL become of me?'

  }

  @CollectionSize.Require(ONE)
  public void testSingletonMapFirst() {
    assertEquals(a, navigableMap.firstEntry());
  }

  @MapFeature.Require(SUPPORTS_REMOVE)
  @CollectionSize.Require(ONE)
  public void testSingletonMapPollFirst() {
    assertEquals(a, navigableMap.pollFirstEntry());
    assertTrue(navigableMap.isEmpty());
  }

  @CollectionSize.Require(ONE)
  public void testSingletonMapNearby() {

  }

  @CollectionSize.Require(ONE)
  public void testSingletonMapFirst() {
    assertEquals(a, navigableMap.firstEntry());
  }

  @MapFeature.Require(SUPPORTS_REMOVE)
  @CollectionSize.Require(ONE)
  public void testSingletonMapPollFirst() {
    assertEquals(a, navigableMap.pollFirstEntry());
    assertTrue(navigableMap.isEmpty());
  }

  @CollectionSize.Require(ONE)
  public void testSingletonMapNearby() {

    worked everywhere that I know of except for one place: when running the GWT
    util.concurrent tests under Guava.

    The problem is that GWT responds poorly to two .gwt.xml files in the same
    Java package; see
    https://groups.google.com/g/google-web-toolkit-contributors/c/CqYH59Dt_rQ/m/uVGW1QdUsXUJ
    for details.

    The summary is that it ignores one file in favor of the other.

    Iterator<Subscriber> one = registry.getSubscribers("");
    assertEquals(s1, one.next().target);
    assertFalse(one.hasNext());

    one = registry.getSubscribers("");

    registry.register(s2);
    registry.register(o1);

    Iterator<Subscriber> three = registry.getSubscribers("");
    assertEquals(s1, one.next().target);
    assertFalse(one.hasNext());

    worked everywhere that I know of except for one place: when running the GWT
    util.concurrent tests under Guava.

    The problem is that GWT responds poorly to two .gwt.xml files in the same
    Java package; see
    https://groups.google.com/g/google-web-toolkit-contributors/c/CqYH59Dt_rQ/m/uVGW1QdUsXUJ
    for details.

    The summary is that it ignores one file in favor of the other.