Mock objects – Setup method – Test Driven Development

The default behaviour of a Moq Mock object is to stub all methods and properties. This means that a call to that method/property with any parameters will not fail and will return a default value for the particular return type.

You call Setup method for any or all of the following reasons:

• You want to restrict the input values to the method.

public interface ICalculator {
  int Sum(int val1, val2);
}

var mock = new Mock<ICalculator>();
mock.Setup(m=>m.Sum(
  It.IsAny<int>(), //Any value
  3                //value of 3
));

The above setup will match a call to method Sum with any value for val1 and val2 value of 3.

• You want to return a specific value. Continuing with ICalculator example, the following setup will return a value of 10 regardless of the input parameters:

var mock = new Mock<ICalculator>();
mock.Setup(m=>m.Sum(
  It.IsAny<int>(), //Any value
  It.IsAny<int>()  //Any value
)).Returns(10);

• You want to use Mock<T>.VerifyAll() after you setups to verify that all previous setups have been called (once).

var mock = new Mock<ICalculator>();
mock.Setup(m=>m.Sum(
  7, //value of 7
  3                //value of 3
));

mock.Setup(m=>m.Sum(
  5, //value of 5
  3                //value of 3
));

mock.VerifyAll();    

The above code verifies that Sum is called twice. Once with (7,3) and once with (5,3).