public void SendMessageException()
        {
            var mock = new Mock<IDataStore>();
            mock.Setup(o => o.IfUser(It.IsAny<int>())).Returns(false);
            var messengerService = new MessengerService {DataStore = mock.Object};

            try
            {
                messengerService.SendMessage(new Message(1, 2, DateTime.Now, "test"));
            }
            catch (Exception exception)
            {
                Assert.AreEqual("Cann't send message. User not found.", exception.Message);
            }
        }
        public void SendMessage()
        {
            var mock = new Mock<IDataStore>();
            mock.Setup(o => o.IfUser(It.IsAny<int>())).Returns(true);
            var messengerService = new MessengerService {DataStore = mock.Object};
            messengerService.SendMessage(new Message(1, 2, DateTime.Now, "test"));

            mock.Verify(w => w.IfUser(1));
            mock.Verify(w => w.IfUser(2));
            mock.Verify(w => w.AddMessage(It.IsAny<Message>()));
        }