Moq4: Update existing mock using Expression

[soringp]

Hi, I'm trying to use Linq to Mocks to update an existing mock, in the same way I use it to create the mock:

Expression<Func<IClaimContext, bool>> initialSetup = cc => cc.GetClaim() == new Claim(123);

var claimContext = Mock.Of<IClaimContext>(initialSetup);

Assert.AreEqual(123, claimContext.GetClaim().ClaimId);


Expression<Func<IClaimContext, bool>> updateSetup = cc => cc.GetClaim() == new Claim(321);

var mock = Mock.Get(claimContext);

// TO DO: Pass updateSetup to mock...

Assert.AreEqual(321, claimContext.GetClaim().ClaimId);

How should I write the missing code to use "updateSetup" so that my second assert passes?

It works with this, instead of using the expression,

mock.Setup(cc => cc.GetClaim()).Returns(new Claim(321));

but if I have multiple setups the code would look much better with Linq to Mocks, and I want to pass the expression as a parameter.

Thanks

[kzu]

I think defining what it means to update can get quite tricky really fast, and expectations will fall short all over. For example, are you intending to replace _all_ method calls or are you going to match by parameters too and only replace those that match with the update expression?

I agree the feature looks interesting. Something like mock.Update(expression)...

[soringp]

An Update method that gets an expression and changes the returned value for matched parameters would be nice. It should do the the same thing as mock.Setup().Returns(), but in a compact way.
It's actually a setup, but Setup already has a signature what gets an expression, but does something else.

[stakx]

@soringp: I agree that the update expression should be treated & have the same effect as several combined Setups.

I'd like to bring up one additional point. Like @davidshen84 suggested in #229, this is obviously a convenience feature (it doesn't do anything that Moq can't already do some other way, but it does it in a more compact way), therefore it should be convenient to use. Given that Mock.Of<T> doesn't return a Mock on which you could immediately call mock.Update, it should be possible to call Update without having to go through Mock.Get first. Therefore I propose that the new method be made static, i.e.:

partial class Mock
{
    public static void Update<T>(T mocked, Expression<Func<T, bool>> updateExpression);
}

Any opinions on this?

[stakx]

Is anyone still interested in this feature at all?

[soringp]

@stakx Sorry for the delay, but yes, I'm still interested in this feature and I like the proposed method.

As a side note, I like compact code and this proposed Update will look very nice, but I have some reservations regarding the expression syntax. For the untrained eye it looks a bit dodgy. Too bad we cannot replace == with a more meaningful operator.

If you add this method I think I will also add a local extension to update the mock:

public static void Update<T>(this Mock<T> mock, Expression<Func<T, bool>> expression) where T:class
{
     Mock.Update(mock.Object, expression);
}

Thanks for your interest in this.

[stakx]

Too bad we cannot replace == with a more meaningful operator.

It is indeed too late for that kind of change. But I'm curious, which operator would've been more meaningful in your opinion, and why?

[soringp]

The assignment operator or the lambda operator could have been good alternatives but the first is not allowed in expressions and I don't see how you could use the latter without some language changes.

It was just a silly idea, only equals works. I guess I was thinking more of using an alias or a custom operator, but this is not possible with C# so case closed :)

[Arithmomaniac]

I think I would name the method SetupSo (SetupSuchThat?). That would emphasize that the expression is what you want to happen to your mock.

[stakx]

Closing this dormant issue, but marking it as "unresolved" so it can be easily found again. Please see #642 for details. If you'd like to pick this up and work on it, please post here briefly and we'll see what we can do!