return "z";
  }

  @Override
  protected String getValueNotInPopulatedMap() throws UnsupportedOperationException {
    return "26";
  }

  /** Helper assertion comparing two maps */
  private void assertMapsEqual(Map<?, ?> expected, Map<?, ?> map) {
    assertEquals(expected, map);
    assertEquals(expected.hashCode(), map.hashCode());

  /** Annotates a public method that declares subtype assertion. */
  @RequiredModifiers(Modifier.PUBLIC)
  @Retention(RetentionPolicy.RUNTIME)
  @Target(ElementType.METHOD)
  @interface TestSubtype {
    /** Suppresses the assertion on {@link TypeToken#getSubtype}. */
    boolean suppressGetSubtype() default false;

    /** Suppresses the assertion on {@link TypeToken#getSupertype}. */

   * Equivalent to {@link #expectMissing(Object[]) expectMissing}{@code (null)} except that the call
   * to {@code contains(null)} is permitted to throw a {@code NullPointerException}.
   *
   * @param message message to use upon assertion failure
   */
  protected void expectNullMissingWhenNullUnsupported(String message) {
    try {
      assertFalse(message, actualContents().contains(null));
    } catch (NullPointerException tolerated) {

      @Override
      public int hashCode() {
        return 1;
      }
    }
  }

  private static void assertContains(String expectedSubstring, String actual) {
    // TODO(kevinb): use a Truth assertion here
    if (!actual.contains(expectedSubstring)) {
      fail("expected <" + actual + "> to contain <" + expectedSubstring + ">");
    }
  }

    return "z";
  }

  @Override
  protected String getValueNotInPopulatedMap() throws UnsupportedOperationException {
    return "26";
  }

  /** Helper assertion comparing two maps */
  private void assertMapsEqual(Map<?, ?> expected, Map<?, ?> map) {
    assertEquals(expected, map);
    assertEquals(expected.hashCode(), map.hashCode());

      assertTrue(e.getMessage().contains("toString representation"));
    }
  }

  private static void assertErrorMessage(Throwable e, String message) {
    // TODO(kevinb): use a Truth assertion here
    if (!e.getMessage().contains(message)) {
      fail("expected <" + e.getMessage() + "> to contain <" + message + ">");
    }
  }

  /**

  }

  /**
   * Asserts that {@code transformation} is horizontal with the given value of {@code y}. Includes
   * assertions about all the public instance methods of {@link LinearTransformation}, including an
   * assertion that {@link LinearTransformation#transform} and {@link LinearTransformation#slope} on
   * its inverse throws as expected.
   */
  static void assertHorizontalLinearTransformation(LinearTransformation transformation, double y) {

    return "z";
  }

  @Override
  protected String getValueNotInPopulatedMap() throws UnsupportedOperationException {
    return "26";
  }

  /** Helper assertion comparing two maps */
  private void assertMapsEqual(Map<?, ?> expected, Map<?, ?> map) {
    assertEquals(expected, map);
    assertEquals(expected.hashCode(), map.hashCode());

    // is cancelled.
    future1.cancel(false);

    // Give the second task a chance to (incorrectly) start up while the first task is running.
    // (This is the assertion that fails.)
    assertThat(future2.isDone()).isFalse();

    // Stop the first task. The second task should then run.
    blockingCallable.stop();
    executor.shutdown();

    // is cancelled.
    future1.cancel(false);

    // Give the second task a chance to (incorrectly) start up while the first task is running.
    // (This is the assertion that fails.)
    assertThat(future2.isDone()).isFalse();

    // Stop the first task. The second task should then run.
    blockingCallable.stop();
    executor.shutdown();