public ClassloaderBuilder newClassloader(String key) {
    return newClassloader(key, getSystemClassloader());
  }
@Test
  public void fail_to_create_the_same_classloader_twice() throws Exception {
    sut.newClassloader("the-cl");
    try {
      sut.newClassloader("the-cl");
      fail();
    } catch (IllegalStateException e) {
      assertThat(e).hasMessage("The classloader 'the-cl' already exists. Can not create it twice.");
    }
  }