public void expectErrorsForTag(String tag) {
    if (UNPREVENTABLE_TAGS.contains(tag)) {
      throw new AssertionError("Tag `" + tag + "` is already suppressed.");
    }
    expectedTags.add(tag);
  }
@Test
  public void testNoExpectedTagFailsTest() {
    expectedException.expect(AssertionError.class);
    rule.expectErrorsForTag("Mytag");
  }