Add an helper class to simplify parameter capture

[ocoanet]

It is frequently required to capture a mock parameter to perform complex assertions. Parameter capture is a regular request from new Moq users.

It can be done with setups and callbacks, but the syntax can be tricky, especially for methods with many parameters.

This helper class simplifies parameter capture:

// Arrange
var capture = new MockCapture<string>();
mock.Setup(x => x.DoSomething(capture.CaptureAny()));

// Act
// ...

// Assert
Assert.Equal("World!", capture.Last);

[ocoanet]

It was not easy to name the class members, for example the AsParameter method can be simply called Capture. The RunOnCapture and CopyOnCapture methods can also be renamed or changed to delegate properties.

I am open to any suggestion or comment.

[kzu]

Need to think a bit more about this, but it looks interesting... Maybe others can chime in too for feedback?

[hahn-kev]

This would be really cool, I would like to see matching support with this though, currently it just matches all, while that's the typical use case I've had cases for other captures. You might also want to get the argument for a specific call, so provide index access to the underlying list.

[ocoanet]

@hahn-kev I updated the PR to include match support. The new syntax is

• mock.Setup(x => x.DoSomething(capture.CaptureAny())) or
• mock.Setup(x => x.DoSomething(capture.Capture(p => p.StartsWith("W"))))

[kzu]

I'd expose IList to make this more flexible, maybe wrapping a ReadOnlyList?

[ocoanet]

Done

[ocoanet]

I removed the underscores on the private field names to follow the naming rules of the project, sorry about that.

[kzu]

I think capture.Any() reads better, and since there is already a Linq Enumerable.Any() and an overload Enumerable.Any(func predicate), I'd propose to make this method and Capture both named Any

[ocoanet]

I choosed the names CaptureAny and Capture to match IsAny and Is methods but I also like your idea to have only one method name with overloads. However, I think Any is confusing because the class exposes captured values through methods like All or Last. Those methods could be renamed but it seems to me that naming the capture method Capture is more straightforward. What do you think ?

[ocoanet]

Ok, I decided to refactor everything to take your remarks into account.

I removed MockCapture, there are now two new classes:

• Capture, a static class that can be used to create simple captures.
• CaptureMatch<T>, a match class that can run a callback on parameter values.

The main use case is now straightforward:

// Arrange
var mock = new Mock<IFoo>();
var items = new List<string>();
mock.Setup(x => x.DoSomething(Capture.In(items)));

// Act
// ...

// Assert
var expectedValues = new List<string> { "Hello!" };
Assert.Equal(expectedValues, items);

Advanced use cases are still supported using CaptureMatch<T>:

var mock = new Mock<IFoo>();
var captureMatch = new CaptureMatch<string>(s => CustomCode(s));
mock.Setup(x => x.DoSomething(Capture.With(captureMatch)));

[kzu]

Beautiful!

Thanks a lot!

[kzu]

btw, are you https://twitter.com/ocoanet?

[kzu]

Shipped! https://www.nuget.org/packages/Moq/4.5.10