@Test
    public void testMissingKerberosAuthenticator() {
        val kerberosClient = new DirectKerberosClient(null);
        TestsHelper.initShouldFail(kerberosClient, "authenticator cannot be null");
    }
Tests the Kerberos client with mocked Kerberos authenticator/validator (i.e. no real tickets used)

@author Garry Boyce
@author Vidmantas Zemleris
@since 2.1.0
pac4j-kerberos/src/test/java/org/pac4j/kerberos/client/direct/KerberosClientTests.java