Getting started with moq

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Remarks

Moq is a mocking library for .Net. It allows interactions with dependencies to be simulated and verified in order to facilitate unit testing.

Release notes for different version of Moq can be found here.

Installation or Setup

  1. Select the project you want to add the reference to Moq.
  2. Open Nuget for this project.
  3. Select "Browse" than type "moq" at the search box.
  4. Select "Moq" and than click on Install.

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Following these steps will install the Moq package and will add a reference to it in the selected project references. After completing these steps Moq can be used in the unit test project by simply declaring it in the test classes files:

Using Moq;
 

Moqs are test doubles

Mocks are meant as test doubles, that allow interactions with the mocks to be validated, they are not meant to replace the system you are testing. Examples will often demonstrate features of Moq as follows:

// Create the mock
var mock = new Mock<IMockTarget>();

// Configure the mock to do something
mock.SetupGet(x => x.PropertyToMock).Returns("FixedValue");

// Demonstrate that the configuration works
Assert.AreEqual("FixedValue", mock.Object.PropertyToMock);

// Verify that the mock was invoked
mock.VerifyGet(x => x.PropertyToMock);
 

Whilst this example shows the steps involved in using the mock, it is important to remember that it doesn't actually test anything, other than that the mock has been setup and used correctly. An actual test that makes use of a mock will supply the mock to the system that is to be tested. To test the following method:

public class ClassToTest
{
    public string GetPrefixedValue(IMockTarget provider)
    {
        return "Prefixed:" + provider.PropertyToMock;
    }
}
 

It is possible to create a mock of the dependent interface:

public interface IMockTarget
{
    string PropertyToMock { get; }
}
 

To create a test that actually validates the behaviour of the GetPrefixedValue method:

// Create and configure the mock to return a known value for the property
var mock = new Mock<IMockTarget>();
mock.SetupGet(x => x.PropertyToMock).Returns("FixedValue");

// Create an instance of the class to test
var sut = new ClassToTest();

// Invoke the method to test, supplying the mocked instance
var actualValue = sut.GetPrefixedValue(mock.Object);

// Validate that the calculated value is correct
Assert.AreEqual("Prefixed:FixedValue", actualValue);

// Depending on what your method does, the mock can then be interrogated to
// validate that the property getter was called.  In this instance, it's
// unnecessary since we're validating it via the calculated value.
mock.VerifyGet(x => x.PropertyToMock);
 

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Friday, October 21, 2016
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