@Test
public void getProxyTicket_NullAttributePrincipal_IllegalStateException() {

    String service = "http://httpbin.org/get";
    Assertion assertion = mock(Assertion.class);
    when(assertionProvider.getAssertion()).thenReturn(assertion);
    when(assertion.getPrincipal()).thenReturn(null);
    assertThatThrownBy(() -> proxyTicketProvider.getProxyTicket(service))
            .isInstanceOf(IllegalStateException.class)
            .hasMessage("Unable to provide a proxy ticket with null %s", AttributePrincipal.class.getSimpleName());
    verify(assertionProvider, times(1)).getAssertion();
    verify(assertion, times(1)).getPrincipal();
}