Unit Test a Catch Block

Question

How to unit test the below catch block?

Below is my controller definition:

public class RunController : Controller
{ 
    Public ActionResult GetExtraRun() 
    { 
        try{ 
             return View("ExtraRun"); 
        } catch(Exception ex) 
        { 
             _log.Error("Index -" + ex.Message, ex); 
             TempData[ErrorInfo] = GetErrorInfo(ex, "RunStatus"); 
             return RedirectToAction("Index", "RunErrorHandling"); 
        } 
     } 
}

I am using NUnit and Moq latest with Asp.NET Core MVC 3.0 version.

So I will have two test case as below

) To check it is return View successfully.
) I need to check catch block as a part of code coverage.

So I need help in 2nd point in the above given code.

Depending on the unit test you run, you will expect different result depending on if it is a catch or not. Then you could test, for example calling the method working and calling the method trowing an exception. If the returned data, for example contains the action result returned on the catch and you were expecting to go there then it will be ok. But anycase for testing better you should have a look into dependancy injection and mocks : https://stackoverflow.com/questions/2665812/what-is-mocking — Mr.Deer, Feb 24 '20 at 13:05
As a code coverage part I need to do that. In that sense could you help? — DT_2, Feb 24 '20 at 13:23

Nkosi · Accepted Answer · 2020-02-25T13:52:36.080

In order to test the desired block of code you would need to make the controller throw an exception when

return View("ExtraRun");

is invoked.

This can be done by mocking the controller and overriding the View(string) function, which is virtual

[Microsoft.AspNetCore.Mvc.NonAction]
public virtual Microsoft.AspNetCore.Mvc.ViewResult View (string viewName);

The following example used MOQ to mock the controller and override the intended function so that the controller behaved as expected when the test was exercised.

//Arrange
//...
var mock = new Mock<RunController>({inject dependencies here});
mock.CallBase = true;

var exception = new Exception("Sample message");

mock.Setup(_ => _.View(It.IsAny<string>())).Throws(exception);

RunController controller = mock.Object;

//Act
var actual = controller.GetExtraRun() as RedirectToActionResult;

//Assert
actual.Should().NotBeNull(); //FluentAssertions

//...perform desired assertions here

Normally the subject under test is not mocked when unit testing. This case however required calling a member within the subject that needed to be configured to behave as desired. Which can be done by overriding it in a derived class. The same could have been done manually without the mocking framework but the framework simplifies the setup.

Unit Test a Catch Block

1 Answers1