Moq setup causing null

I'm new to Unit Testing, and Moq, so if I'm completely wrong in my method or understanding, please assist me.

I have a logic method I am testing. I've commented out the logic, but all it does is check a few values in the 'model' and returns if there's a problem. In the case we're looking at, there's no problem.

        public ReplyDto SaveSettings(SnowballDto model)
        {

            // Some logic here that reads from the model.

            var result = _data.SaveSettings(model);
            return result;
        }

My test, using NUnit and MOQ, looks like this:

_logic = new SnowballLogic(mockSnowballData.Object, mockLog.Object);

           mockSnowballData
                .Setup(x => x.SaveSettings(SnowballDto_Good))
                .Returns(new ReplyDto {
                    IsSuccess = true,
                    Message = "Saved",
                    ReplyKeyID = 1
                });

In each test, I call a private setup function that sets up the things I'll be using.

 private void SetupData()
        {
            SnowballDto_Good = new SnowballDto {
                FirstPaymentDate = DateTime.UtcNow,
                ID = 1,
                OrderedIDPriority = new List<int>(),
                SnowballTypeID = 1,
                TargetPayment = 1000
            };

            DebtDtoList_ThreeDebt.Clear();
            DebtDtoList_ThreeDebt.Add(new DebtDto { ID = 1, Description = "Debt 1", ManualSnowballPriority = 1, MinimumMonthlyPaymentAmount = 140, OpeningBalance = 5000, RunningData = new DebtRunningDto { Balance = 5000 }, OpeningDate = DateTime.UtcNow, SnowballID = 1, StandardRate = 10 });
            DebtDtoList_ThreeDebt.Add(new DebtDto { ID = 2, Description = "Debt 2", ManualSnowballPriority = 2, MinimumMonthlyPaymentAmount = 90, OpeningBalance = 1600, RunningData = new DebtRunningDto { Balance = 1600 }, OpeningDate = DateTime.UtcNow, SnowballID = 1, StandardRate = 15 });
            DebtDtoList_ThreeDebt.Add(new DebtDto { ID = 3, Description = "Debt 3", ManualSnowballPriority = 3, MinimumMonthlyPaymentAmount = 300, OpeningBalance = 9000, RunningData = new DebtRunningDto { Balance = 9000 }, OpeningDate = DateTime.UtcNow, SnowballID = 1, StandardRate = 20 });


        }

So, my understanding of MOQ is that I am saying "When the SnowballData class's "SaveSettings" methid is called, and a "SnowballDto_Good" object is passed in, always return a new ReplyDto with IsSuccess = true.

Therefore, when I make the call:

var result = _data.SaveSettings(model);

It should return ReplyDto with IsSuccess = true

However, when I put a breakpoint in when I call 'SaveSettings', it returns null all the time.

If I change my setup to:

.Setup(x => x.SaveSettings(It.IsAny<SnowballDto>()))

The test passes. Why is it returning null when I give it a real SnowballDto?

---

well, it seems you are passing an instance of SnowballDto named model in the "act" part of your test

var result = _data.SaveSettings(model);

In the setup of moq, however, you configure it to return a new ReplyDto only when the instance SnowballDto_Good is specified to SaveSettings . In all other cases, the method's mock is not configured, and - in case of a loose mocking strategy (the default) - it will return the default value for SaveSettings return type. In this case: null.

When you're using It.IsAny<SnowballDto> you are basically telling moq to configure SaveSettings to return a new instance not only then the instance SnowballDto_Good is passed to it, but any instance of that type.

What you need to do is to change your "act" part of your test as follows:

var result = _data.SaveSettings(SnowballDto_Good);

then it will work with your original mock setup, because the correct instance will be passed to SaveSettings .

This is precisely why I like to instantiate my mocks using MockBehavior.Strict.

Instead of returning null, it will throw an exception that will tell you that you didn't configure your mock correctly.

Hope this helps.

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