@Test public void testFindCustomerById() { Customer c1 = new Customer(); c1.setId(1L); doReturn(c1).when(customerDaoMock).findById(1L); Customer customer = service.findCustomerById(1L); verify(customerDaoMock).findById(1L); verifyNoMoreInteractions(customerDaoMock); Assert.assertEquals(Long.valueOf(1), customer.getId()); }