@Test
public void testUserExistsInAllEngines() {

    boolean result = engineManager.userExists("user");
    verify(engine, times(1)).userExists("user");
    assertTrue(result);
    when(engine.userExists(anyString())).thenReturn(false);
    result = engineManager.userExists("user");
    verify(engine, times(2)).userExists("user");
    assertFalse(result);
}