Unit testing IActionResult

ControllerTestBase.cs

public class ControllerTestBase 
{
  protected void Is<T>(IActionResult result, HttpStatusCode statusCode) where T : StatusCodeResult
  {
      var r = result as T;
      r.Should().NotBeNull();
      r.StatusCode.Should().Be((int)statusCode);
  }

  protected TPayload Is<TResult, TPayload>(IActionResult result, HttpStatusCode statusCode) where TResult : ObjectResult
  {
      var r = result as TResult;
      r.Should().NotBeNull();
      r.StatusCode.Should().Be((int)statusCode);
      r.Value.Should().BeAssignableTo<TPayload>();
      return (TPayload)r.Value;
  }
}

MyControllerTest.cs

public class MyControllerTest: ControllerTestBase
{
  [Fact(DisplayName="MyMethod should return NoContent if everything goes well")]
  public async Task MyMethod_NoErrors_ReturnsNoContent()
  {
    var myService = new Mock<IMyService>();
    myService.Setup(ms => ms.ServiceMethod(It.IsAny<string>())).ReturnsAsync(true);
    var myController = new MyController(myService.Object);
    
    var result = await myController.MyMethod("potato");
    
    Is<NoContentResult>(result, HttpStatusCode.NoContent);    
  }

  [Fact(DisplayName="MyMethod should return InternalServerError if MyService throws an exception")]
  public async Task MyMethod_NoErrors_ReturnsNoContent()
  {
    var myService = new Mock<IMyService>();
    myService.Setup(ms => ms.ServiceMethod(It.IsAny<string>())).ThrowsAsync(new Exception());
    var myController = new MyController(myService.Object);
    
    var result = await myController.MyMethod("potato");
    
    Is<InternalServerErrorResult>(result, HttpStatusCode.InternalServerError);
  }
  
  
  [Fact(DisplayName="MyResultMethod should return Ok if everything goes well")]
  public async Task MyResultMethod_NoErrors_ReturnsOk()
  {
    string expected = "pancakes";
    var myService = new Mock<IMyService>();
    myService.Setup(ms => ms.ServiceResultMethod(It.IsAny<string>())).ReturnsAsync(expected);
    var myController = new MyController(myService.Object);
    
    var result = await myController.MyResultMethod("potato");
    
    // Provide the ObjectResult type and the expected payload type
    var stringResult = Is<OkObjectResult, string>(result);
    stringResult.Should().Be(expected);
  }
}