String getLoginUrl() {
    return configuration.get(LOGIN_URL).orElseThrow(() -> new IllegalArgumentException("Login URL is missing"));
  }
@Test
  public void fail_to_get_login_url_when_null() {
    assertThatThrownBy(() -> underTest.getLoginUrl())
      .isInstanceOf(IllegalArgumentException.class)
      .hasMessage("Login URL is missing");
  }