C# – Mock a method of the subject under test in Moq

cmockingmoq

I want to test method A of my class, but without calling the actual method B which is normally called by A. That's because B has a lot of external interactions I don't want to test for now.

I could create mocks for all the services called by B, but that's quite some work. I'd rather just mock B and make it return sample data.

Is that possible to do with Moq framework?

Best Answer

It is, with a catch! You have to make sure method B is virtual and can be overriden.

Then, set the mock to call the base methods whenever a setup is not provided. Then you setup B, but don't setup A. Because A was not setup, the actual implementation will be called.

var myClassMock = new Mock<MyClass>();
myClassMock.Setup(x => x.B()); //mock B

myClassMock.CallBase = true;

MyClass obj = myClassMock.Object;
obj.A(); // will call the actual implementation
obj.B(); // will call the mock implementation

Behinds the scenes, Moq will dynamically create a class that extends MyClass and overrides B.

From Martin Fowler about Mock and Stub

Fake objects actually have working implementations, but usually take some shortcut which makes them not suitable for production

Stubs provide canned answers to calls made during the test, usually not responding at all to anything outside what's programmed in for the test. Stubs may also record information about calls, such as an email gateway stub that remembers the messages it 'sent', or maybe only how many messages it 'sent'.

Mocks are what we are talking about here: objects pre-programmed with expectations which form a specification of the calls they are expected to receive.

From xunitpattern:

Fake: We acquire or build a very lightweight implementation of the same functionality as provided by a component that the SUT depends on and instruct the SUT to use it instead of the real.

Stub : This implementation is configured to respond to calls from the SUT with the values (or exceptions) that will exercise the Untested Code (see Production Bugs on page X) within the SUT. A key indication for using a Test Stub is having Untested Code caused by the inability to control the indirect inputs of the SUT

Mock Object that implements the same interface as an object on which the SUT (System Under Test) depends. We can use a Mock Object as an observation point when we need to do Behavior Verification to avoid having an Untested Requirement (see Production Bugs on page X) caused by an inability to observe side-effects of invoking methods on the SUT.

Personally

I try to simplify by using : Mock and Stub. I use Mock when it's an object that returns a value that is set to the tested class. I use Stub to mimic an Interface or Abstract class to be tested. In fact, it doesn't really matter what you call it, they are all classes that aren't used in production, and are used as utility classes for testing.

C# – How to verify that method was NOT called in Moq

Run a verify after the test which has a Times.Never enum set. e.g.

_mock.Object.DoSomething()
_mock.Verify(service => service.ShouldntBeCalled(), Times.Never);

Best Answer

Related Solutions

What’s the difference between faking, mocking, and stubbing

From Martin Fowler about Mock and Stub

From xunitpattern:

Personally

C# – How to verify that method was NOT called in Moq

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