[moq] Mock delegate

 C#   Unit test   moq   delegate

▌Introduction

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This article shows how to mock delegate for unit-testing.

▋Related articles

1.  [moq] Mock object and Mock.of

2.  [moq] Mock delegate

3.  [moq] Mock a non-interface object

▌Environment

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▋Visual Studio 2017 community

▋dotnet core 2.2.101

▋Moq 4.10.1

▌Implement

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We will test the Get(…) function of class, DataAccessService<T> which implements interface, IDataAccessService<T>.  It has a delegate, AuthorizeEvent, which we will mock in this test.

The unit test’s goal:

1.  Test Get(…) function’s accuracy

2.  The delegate is called

▋Interfaces and Classes

▋IDataAccessService.cs

public delegate bool Authorize(string caller);

  public interface IDataAccessService<T>

  {

        string ConnectionStr { get; set; }

        event Authorize AuthorizeEvent;

        T Get(string id);

  }

▋DataAccessService.cs

public class DataAccessService<T> : IDataAccessService<T> where T:new()

    {

        private readonly string _caller = "DataAccessService";

        public string ConnectionStr { get; set; }

        public event Authorize AuthorizeEvent;

        public DataAccessService()

        {

        }

        public T Get(string id)

        {

            //HACK: Implement the logic here to replace the below line

                if (this.AuthorizeEvent(this._caller) == true)

                    return new T();

                else

                    return default(T);

        }

    }

▋Unit test without mocking the delegate

Lets see a bad idea of not mocking the delegate in the unit test.

That means we have to create a method as a reference for the delegate, and a static flag to make sure the delegate is triggered.

private static bool callbackIsTriggered = false;

[Test]

  public void TestGet()

  {

            IDataAccessService<Birthday> dataAccess = new DataAccessService<Birthday>();

            #region Use the real method

            dataAccess.AuthorizeEvent += MySaveLogAction;

            var rtn = dataAccess.Get(It.IsAny<string>());

            Assert.IsTrue(callbackIsTriggered);

            Assert.IsFalse(rtn == null);

            #endregion

 }

 private static bool MySaveLogAction(string caller)

 {

            Debug.WriteLine($"Called from {caller}");

            callbackIsTriggered = true;

            return true;

 }

    }

▋Unit test by mocking delegate with moq

We will use moq to mock the delegate, so that we can focus on tesing the IDataAccessService.Get() function.

[Test]

  public void TestGet()

  {

            IDataAccessService<Birthday> dataAccess = new DataAccessService<Birthday>();

            #region Mock the callback

            var mockCallback = new Mock<Authorize>();

            mockCallback.Setup(x => x(It.IsAny<string>())).Returns(true);

            dataAccess.AuthorizeEvent += mockCallback.Object;

            dataAccess.Get(It.IsAny<string>());

            mockCallback.Verify(x => x(It.IsAny<string>()), Times.Once);

Assert.IsFalse(rtn == null);

            #endregion

  }

The above code mocks the delegate: Authorize, and setup the returning value. (If the delegate returns nothing, then ignore .Returns(…)) in this line:

mockCallback.Setup(x => x(It.IsAny<string>())).Returns(true);

And notice we CANNOT directly mock the Invoke method of a delegate like this:

 mockCallback.Setup(x => x.Invoke(It.IsAny<string>())).Returns(true);

Which will cause the error:

System.InvalidCastException : Unable to cast object of type 'System.Linq.Expressions.InstanceMethodCallExpression1' to type 'System.Linq.Expressions.InvocationExpression'.

▌Reference

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