@Test
  public void testAstWithoutChildren() {
    final SuppressWarningsHolder holder = new SuppressWarningsHolder();
    final DetailAST methodDef = new DetailAST();
    methodDef.setType(TokenTypes.METHOD_DEF);

    try {
      holder.visitToken(methodDef);
      fail("Exception expected");
    } catch (IllegalArgumentException ex) {
      assertEquals("Identifier AST expected, but get null.", ex.getMessage());
    }
  }