void testGetKeys_WithKeys() throws LoginException {
        Set<Object> privateCredentials = new HashSet<>();
        privateCredentials.add(key1);
        privateCredentials.add(key2);
        when(subject.getPrivateCredentials()).thenReturn(privateCredentials);

        try (MockedConstruction<LoginContext> mocked = Mockito.mockConstruction(LoginContext.class, (mock, context) -> {
            when(mock.getSubject()).thenReturn(subject);

     *
     * @return array of KerberosKey objects
     */
    public KerberosKey[] getKeys() {
        List<Key> serverKeys = new ArrayList<>();

        Set<Object> serverPrivateCredentials = this.subject.getPrivateCredentials();
        for (Object credential : serverPrivateCredentials) {
            if (credential instanceof KerberosKey) {
                serverKeys.add((KerberosKey) credential);
            }
        }