Question

For unit testing purposes I want to provide a mock for a javax.security.auth.kerberos.KerberosTicket instance. I tried using Mockito and PowerMockito but both failed with a similar message:

org.mockito.exceptions.misusing.MissingMethodInvocationException: 
when() requires an argument which has to be 'a method call on a mock'.
For example:
    when(mock.getArticles()).thenReturn(articles);

Also, this error might show up because:
1. you stub either of: final/private/equals()/hashCode() methods.
   Those methods *cannot* be stubbed/verified.
2. inside when() you don't call method on mock but on some other object.

Adding @RunWith and @PrepareForTest annotations results in following LinkageException:

java.lang.LinkageError:
  loader constraint violation: 
  when resolving method "sun.security.jgss.krb5.Krb5Util.getTicketFromSubjectAndTgs(ILjava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/security/AccessControlContext;)Ljavax/security/auth/kerberos/KerberosTicket;"
  the class loader (instance of org/powermock/core/classloader/MockClassLoader) of the current class, 
  org/epo/security/spnego/impl/KerberosUtilsTest, and the class loader (instance of <bootloader>) 
  for resolved class, sun/security/jgss/krb5/Krb5Util, have different Class objects 
  for the type javax/security/auth/kerberos/KerberosTicket used in the signature

My test class looks like this:

@RunWith(PowerMockRunner.class)

@PrepareForTest({KerberosTicket.class})
public class KerberosUtilsTest {

@Test
public void testGetTicketFromSubjectAndTgs() throws LoginException, KrbException, IOException {
    PowerMockito.mockStatic(Krb5Util.class);
    KerberosTicket kerberosTicketMock = PowerMockito.mock(KerberosTicket.class);

    AccessControlContext controlContext = AccessController.getContext();

    // Causes the LinkageError to be thrown
    when(Krb5Util.getTicketFromSubjectAndTgs(-1, "test", "test", "test", controlContext)).thenReturn(
                kerberosTicketMock);

    KerberosTicket actual = new KerberosUtils().getTicketFromSubjectAndTgs(-1, "test", "test", "test",
                controlContext);

    assertEquals(kerberosTicketMock, actual);
}

Searching internet revealed that the LinkageError can be fixed by changing the annotation as such:

@PowerMockIgnore({"sun.security.jgss.krb5.Krb5Util", "javax.security.auth.kerberos.KerberosTicket"})
@PrepareForTest({KerberosUtils.class})
@RunWith(PowerMockRunner.class)

Running this gets me back to square one:

org.mockito.exceptions.misusing.MissingMethodInvocationException: 
when() requires an argument which has to be 'a method call on a mock'.
For example:
    when(mock.getArticles()).thenReturn(articles);

Also, this error might show up because:
1. you stub either of: final/private/equals()/hashCode() methods.
   Those methods *cannot* be stubbed/verified.
2. inside when() you don't call method on mock but on some other object.

Does someone have a solution for this?

Answer 1

Most of the methods of KerberosTicket are final, but PowerMockito should be able to mock them.

Don’t forget to annotate your test class as required by PowerMockito to mock final methods

@RunWith(PowerMockRunner.class)
@PrepareForTest(KerberosTicket.class)

and use PowerMockito instead of Mockito inside a test

KerberosTicket mock = PowerMockito.mock(KerberosTicket.class);
PowerMockit.when(mock.getAuthTime().thenReturn(...);