In previous posts we saw how to get started testing ASP.NET Core MVC controllers and also how to use the Moq mocking library in .NET Core tests.

If there is code in controllers that needs testing, but the controller has a dependency, for example passed into the constructor, it may not make sense to use the real version of the dependency. In these cases Moq can be used to create a mock version of the dependency and pass it to the controller that needs testing.

As an example suppose we have the following controller code:

public class HomeController : Controller
{
    private readonly ISmsGateway _smsGateway;

    public HomeController(ISmsGateway smsGateway)
    {
        _smsGateway = smsGateway;
    }

    [HttpPost]
    [ValidateAntiForgeryToken]
    public IActionResult Send(SendSmsRequest request)
    {
        if (ModelState.IsValid)
        {
            var sendReceipt = _smsGateway.Send(request.PhoneNumber, request.Message);

            return Ok(sendReceipt);
        }

        return BadRequest();
    }
}

In the preceding code, the controller takes an ISmsGateway dependency as a constructor parameter. This dependency is later used in the the Send() method.

After installing Moq a mock SMS gateway can be created. Once created, Moq’s Setup() method can be used to determine what happens when the controller calls the mocked Send() method as the following code demonstrates:

[Fact]
public void ShouldSendOk()
{
    SendSmsRequest sendSmsRequest = new SendSmsRequest
    {
        PhoneNumber = "42",
        Message = "Hello"
    };

    Guid expectedSendReceipt = Guid.NewGuid();

    var mockSmsGateway = new Mock<ISmsGateway>();
    
    mockSmsGateway.Setup(x => x.Send(sendSmsRequest.PhoneNumber, sendSmsRequest.Message))
                  .Returns(expectedSendReceipt);

    var sut = new HomeController(mockSmsGateway.Object);
    
    IActionResult result = sut.Send(sendSmsRequest);

    var okObjectResult = Assert.IsType<OkObjectResult>(result);

    Assert.Equal(expectedSendReceipt, okObjectResult.Value);
}

We may also want to test that if there is a model binding error, then  no message is sent via the SMS gateway. The follow test code shows the use of the AddModelError() method to simulate an error, and the use of Moq’s Verify() method to check that the gateway’s Send() method was never called:

[Fact]
public void ShouldNotSendWhenModelError()
{
    SendSmsRequest sendSmsRequest = new SendSmsRequest
    {
        PhoneNumber = "42",
        Message = "Hello"
    };

    var mockSmsGateway = new Mock<ISmsGateway>();

    var sut = new HomeController(mockSmsGateway.Object);
    sut.ModelState.AddModelError("Simulated", "Model error");

    sut.Send(sendSmsRequest);

    mockSmsGateway.Verify(x => x.Send(It.IsAny<string>(), It.IsAny<string>()), Times.Never);
}

To learn more about using Moq to create/configure/use mock objects check out:

• My Mocking with Moq and NUnit Pluralsight course
• My Mocking with Moq and xUnit Pluralsight course

You can start watching with a Pluralsight free trial.

SHARE: