单个方法或通用 It.IsAny 的模拟行为松散

Question

I have an abstract class Shape and a couple of classes inheriting from it ( Square , Rectangle , Triangle , Circle , ...). I also have an AreaCalculator class, which contains a method named CalculateAreasByShape() . This method calls a series of CalculateShapeAreas<TShape>(List<TShape> shapes) methods for each Shape type.

Now, in my unit tests, I have the following code:

...
var areaMock = new Mock<AreaCalculator>(MockBehavior.Strict);
areaMock.Setup(m => m.CalculateAreasByShape()).Returns(new Dictionary<Type, decimal>());
var canvas = new DemoCanvas(shapes, perimeterMock.Object, areaMock.object);
var result = canvas.RunShapeCalculations();
...

This code fails on the fact, that MockBehavior is set to Strict and there is no setup for the CalculateShapeAreas<TShape>() methods. Now, I know I could run a setup for each of the Shape types, eg:

areaMock.Setup(m => m.CalculateShapeAreas<Triangle>(It.IsAny<List<Triangle>>())).Returns(default(decimal));

But this will create a lot of duplicate code. I wonder whether we can use the fact that all shapes inherit from the same base class. I have tried the following, but it does not work:

areaMock.Setup(m => m.CalculateShapeAreas<Shape>(It.IsAny<List<Shape>>())).Returns(default(decimal));

Alternatively, is it possible to set MockBehavior.Loose on a single generic method (meaning, it would not check the actual type)?

Answer 1

It.IsAny for open generic support is not yet present in the moq (release 4.12.0). Eventually there are some plans to introduce this, take a look here

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I think problem you are facing is because you are using List<T> as an input parameter. As you might notice List<T> is not covariant.

What that mean?

List<Shape> shapeList;
IEnumerable<Shape> shapeEnumerable;
var triag = new List<Triangle>();

shapeList = triag; // NOT ALLOWED
shapeEnumerable = triag; // ALLOWED

The same makes problem while mocking. One solution could be to change interface and instead of passing List<T> pass IEnumerable<out T> , or as @JeppeStigNielsen pointed out IReadOnlyList<out T> . In fact any covariant in T interface which is implemented by List<T> could be used.

areaMock
    .Setup(m => m.CalculateShapeAreas<Shape>(It.IsAny<IEnumerable<Shape>>()))
    .Returns(default(decimal));