public abstract AppResponse activateApp(AppAuthenticator appAuthenticator, AppSession appSession);
@Test
    void activateAppActualMethodByActivationCodeTest() {
        AppAuthenticator appAuthenticator = new AppAuthenticator();
        appAuthenticator.setActivationCode("");
        appAuthenticator.setGeldigheidstermijn("");

        when(flow.activateApp(any(), any(), anyString())).thenCallRealMethod();
        when(flow.activateApp(any(), any(), anyString(), anyBoolean())).thenCallRealMethod();

        AppResponse result = flow.activateApp(appAuthenticator, mockedAppSession, LETTER);

        assertEquals("active", appAuthenticator.getStatus());
        assertNotNull(appAuthenticator.getActivatedAt());
        assertNull(appAuthenticator.getActivationCode());
        assertNull(appAuthenticator.getGeldigheidstermijn());
        assertTrue(result instanceof ActivateAppResponse);
        assertEquals(20, ((ActivateAppResponse) result).getAuthenticationLevel());
    }