Migrating from Moq to NSubstitute

Mocking is a necessary evil for unit testing.

Fortunately frameworks like NSubstitute make it painless setup your mock services. NSubstitute offers a fluent API that requires few lambdas and no calls to an Object property. You just get back the interface that you are substituting and work with it directly. Frankly, NSubstitute is so easy to work with that it almost seems like magic!

Below is a visual representation of equivalent commands between Moq and NSubstitute:

NSubstitute

[Fact]

public void NSubstitute()

{

    var tester = Substitute.For<ITester>();

--------------------------------------------

    var voidArg = String.Empty;

    tester

        .When(t => t.Void(Arg.Any<string>()))

        .Do(i => voidArg = i.Arg<string>());

    tester.Void("A");

    Assert.Equal("A", voidArg);

--------------------------------------------

    tester

        .Bool()

        .Returns(true);

    var boolResult = tester.Bool();

    Assert.Equal(true, boolResult);

--------------------------------------------

    tester

        .Int

        .Returns(1);

    var intResult = tester.Int;

    Assert.Equal(1, intResult);

--------------------------------------------

    tester.Received(1).Void("A");

--------------------------------------------

    tester.DidNotReceive().Void("B");

}

Moq

[Fact]

public void Moq()

{

    var tester = new Mock<ITester>();

    // Setup a callback for a void method. -------

    var voidArg = String.Empty;

    tester

        .Setup(t => t.Void(It.IsAny<string>()))

        .Callback<string>(s => voidArg = s);

    tester.Object.Void("A");

    Assert.Equal("A", voidArg);

    // Setup the result of a method. -------------

    tester

        .Setup(t => t.Bool())

        .Returns(true);

    var boolResult = tester.Object.Bool();

    Assert.Equal(true, boolResult);

    // Setup the result of a property. -----------

    tester

        .SetupGet(t => t.Int)

        .Returns(1);

    var intResult = tester.Object.Int;

    Assert.Equal(1, intResult);

    // Ensure that a function was called. --------

    tester.Verify(m => m.Void("A"), Times.Once);

    // Ensure that a function was NOT called. ----

    tester.Verify(m => m.Void("B"), Times.Never);

}

Enjoy,
Tom