@Test
    public void testMissingKerberosHeader() {
        val client = new DirectKerberosClient(new KerberosAuthenticator(krbValidator));
        val credentials = client.getCredentials(new CallContext(MockWebContext.create(), new MockSessionStore()));
        assertFalse(credentials.isPresent());
    }
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