c# - How to unit test HttpContext.SignInAsync()?

Question

SignInAsync() Source Code

I ran into some problems with unit testing.

1. DefaultHttpContext.RequestServices is null
2. I tried to create the AuthenticationService object, but I do not know what parameters to pass

What should I do? How to unit test HttpContext.SignInAsync()?

Method under test

public async Task<IActionResult> Login(LoginViewModel vm, [FromQuery]string returnUrl)
{
    if (ModelState.IsValid)
    {
        var user = await context.Users.FirstOrDefaultAsync(u => u.UserName == vm.UserName && u.Password == vm.Password);
        if (user != null)
        {
            var claims = new List<Claim>
            {
                new Claim(ClaimTypes.Name, user.UserName)
            };
            var identity = new ClaimsIdentity(claims, "HappyDog");

            // here
            await HttpContext.SignInAsync(new ClaimsPrincipal(identity));
            return Redirect(returnUrl ?? Url.Action("Index", "Goods"));
        }
    }
    return View(vm);
}

What I have tried so far.

[TestMethod]
public async Task LoginTest()
{
    using (var context = new HappyDogContext(_happyDogOptions))
    {
        await context.Users.AddAsync(new User { Id = 1, UserName = "test", Password = "password", FacePicture = "FacePicture" });
        await context.SaveChangesAsync();

        var controller = new UserController(svc, null)
        {
            ControllerContext = new ControllerContext
            {
                HttpContext = new DefaultHttpContext
                {
                    // How mock RequestServices?
                    // RequestServices = new AuthenticationService()?
                }
            }
        };
        var vm = new LoginViewModel { UserName = "test", Password = "password" };
        var result = await controller.Login(vm, null) as RedirectResult;
        Assert.AreEqual("/Goods", result.Url);
    }
}

Answer 1

HttpContext.SignInAsync is an extension method that uses RequestServices, which is IServiceProvider. That is what you must mock.

context.RequestServices
    .GetRequiredService<IAuthenticationService>()
    .SignInAsync(context, scheme, principal, properties);

You can either create a fake/mock manually by creating classes that derive from the used interfaces or use a mocking framework like Moq

//...code removed for brevity

var authServiceMock = new Mock<IAuthenticationService>();
authServiceMock
    .Setup(_ => _.SignInAsync(It.IsAny<HttpContext>(), It.IsAny<string>(), It.IsAny<ClaimsPrincipal>(), It.IsAny<AuthenticationProperties>()))
    .Returns(Task.FromResult((object)null));

var serviceProviderMock = new Mock<IServiceProvider>();
serviceProviderMock
    .Setup(_ => _.GetService(typeof(IAuthenticationService)))
    .Returns(authServiceMock.Object);

var controller = new UserController(svc, null) {
    ControllerContext = new ControllerContext {
        HttpContext = new DefaultHttpContext {
            // How mock RequestServices?
            RequestServices = serviceProviderMock.Object
        }
    }
};

//...code removed for brevity

You can read up on how to use Moq here at their Quick start

You could just as easily mocked the HttpContext as well like the other dependencies but if a default implementation exists that causes no undesired behavior, then using that can make things a lot simpler to arrange

For example, an actual IServiceProvider could have been used by building one via ServiceCollection

//...code removed for brevity

var authServiceMock = new Mock<IAuthenticationService>();
authServiceMock
    .Setup(_ => _.SignInAsync(It.IsAny<HttpContext>(), It.IsAny<string>(), It.IsAny<ClaimsPrincipal>(), It.IsAny<AuthenticationProperties>()))
    .Returns(Task.FromResult((object)null));

var services = new ServiceCollection();
services.AddSingleton<IAuthenticationService>(authServiceMock.Object);

var controller = new UserController(svc, null) {
    ControllerContext = new ControllerContext {
        HttpContext = new DefaultHttpContext {
            // How mock RequestServices?
            RequestServices = services.BuildServiceProvider();
        }
    }
};

//...code removed for brevity

That way if there are other dependencies, they can be mocked and registered with the service collection so that they can be resolved as needed.