Unit testing middleware with NUnit and NSubstitute - unit-testing

Question

I've written a bit of middleware in an ASP.NET Core site and I'm trying to unit test it, mainly by following this guide that uses Moq.
My problem is finding an NUnit/NSubstitute equivalent for new DefaultHttpContext(). Substituting HttpContext will trigger the middleware, but it passes the try. I presume this is because of the issue quoted below. Does NUnit have a function to create a real HttpContext, or am I looking at a lot more infrastructure to achieve this?
I am sending an instance of DefaultHttpContext to the Invoke method. I can't use a mocked HttpContext in this scenario because the first middleware (the lambda function that we passed to the constructor) will need to write to the response. Hence the HttpResponse needs to be a real object not mocked.
Here is the code for my Test
[TestFixture]
public class ExceptionHelperTests
{
private IErrorRepository errorRepository;
private ExceptionHandler handler;
[SetUp]
public void Setup()
{
errorRepository = Substitute.For<IErrorRepository>();
}
[Test]
public async void Given_AnExceptionHappens_Then_ItShouldBeLogged()
{
// Arrange
const string username = "aUser";
var user = Substitute.For<ClaimsPrincipal>();
user.Identity.Name.Returns(username);
handler = new ExceptionHandler(
next: async (innerHttpContext) =>
{
innerHttpContext.User = user;
},
repository: errorRepository);
// Act
await handler.Invoke(new DefaultHttpContext());
// Assert
errorRepository.Received().LogException(Arg.Any<string>(), Arg.Any<Exception>(), Arg.Is(username));
}
}
Here is the IErrorRepository
public interface IErrorRepository
{
Exception LogException(string message, Exception ex, string userId);
void LogMessage(string message, string errorDetail, string userId);
}
And here is the middleware (with a simplified HandleException):
public sealed class ExceptionHandler
{
private readonly RequestDelegate _next;
private readonly IErrorRepository repository;
public ExceptionHandler(RequestDelegate next, IErrorRepository repository)
{
_next = next;
this.repository = repository;
}
public async Task Invoke(HttpContext context)
{
try
{
await _next(context);
}
catch (Exception ex)
{
HandleException(ex, context.User.Identity.Name);
}
}
public void HandleException(Exception ex, string userId)
{
repository.LogException("An unhandled exception has occurred.", ex, userId);
}
}

Answer 1

DefaultHttpContext is just the default implementation of HttpContext abstract class.
You just could do
var HttpContextSub = Substitute.For<HttpContext>();