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).

Setup method is used to set expectations on the mock object For example:

mock.Setup(foo => foo.DoSomething("ping")).Returns(true);

Here you are setting the DoSomething method on mock object. You are saying, when the parameter is "ping", the method returns true.

Now this object can further act as a mock or a stub depending on your usage. If you want to use it in state based testing, it can act as a stub. If you want to use it in behavior based testing, it can act as a mock. In behavior testing, you will call the verify method on the mock object to assert that the method was called with "ping" parameter

Further refer these links: