Using Xunit in .Net core web API – How to test/ pass 500 status code

We are trying the Test Driven Development for our .Net core 3.1 Web API and using XUnit for the same.

In my controller I have test cases or [Fact] written for the status codes 200,404 and other scenarios.

When it comes to unit testing 500 internal server error – I am not sure how to pass the code, or how to assert it.

It always fails for me by using the below code.

How to successfully test the 500 – Internal server error in my unit test ?

I am very new to TDD any comment is helpful, below is the code :

[Fact] // 404 Sample unit test method
public async Task Get_OnNotFound_Returns404()
{
// Arrange
var mockService = new Mock<IService>();

mockService.Setup(service => service.GetTypes(It.IsAny<string>(), It.IsAny<CancellationToken>())).ReturnsAsync(new List<TypeResponse>());
          

 var sut = new HomeController(mockService.Object);

//Act
var result = await sut.GetSampleMethod("foo") as ObjectResult;

//Assert
       
 Assert.Equal(StatusCodes.Status404NotFound, result.StatusCode);
           
}


// Below is my always failing 500 code unit test

  [Fact]
public async Task Returns_500_When_Returns_Error() 
{
// Arrange
 var mockService = new Mock<IService>();

mockService.Setup(service => service.GetTypes(It.IsAny<string>(), It.IsAny<CancellationToken>())).ReturnsAsync(new List<TypeResponse>());
          
 var sut = new HomeController(mockService.Object);

 //Act
var result = await GetSampleMethod("foo") as ObjectResult;

//Assert
 Assert.Equal(StatusCodes.Status500InternalServerError, result.StatusCode);
}

// Below is my controller method :

[HttpGet]
public async Task<IActionResult> GetSampleMethod(string id, CancellationToken cancellationToken)
{
  try
     {
       var result = await _service.GetSampleMethod(id, cancellationToken);
       if(result.Any())
        {
           return Ok(result);
         }

        return StatusCode(StatusCodes.Status404NotFound, new Error { Message = "No Records ." });
     }
   catch (Exception ex)
   {
    return StatusCode(StatusCodes.Status500InternalServerError, new Error { Message = !string.IsNullOrWhiteSpace(ex.Message) ? ex.Message : "An unhandled error occurred." });
    }
  }
}

>Solution :

It’s clear that your method returns Status500InternalServerError in case of an exception. So you have to mock an exception for it:

mockService.Setup(service => service.GetTypes(It.IsAny<string>(),
     It.IsAny<CancellationToken>()))
       .Throws(new Exception());