如何对依赖于HttpContext.GetGlobalResourceObject的类进行单元测试？

Question

I'm trying to add tests to a webforms project. There's a static method to grab lines from resource files. One of the classes I'm trying to test, relies on grabbing text from the resource file.

public static class MyStaticClass {
    public static string getText(String name)
    {
        String s = HttpContext.GetGlobalResourceObject("MyResources", name).ToString();
        return s;
    }
}

public class ClassUnderTest
{
    // returns: "Hey it's my text"
    private string _eg = MyStaticClass.getText("label_in_resources.resx_file")
}

class UnitTests
{
    [Test]
    public void TestMyClass()
    {
        ClassUnderTest _cut = new ClassUnderTest();
        // errors out because ClassUnderTest utilizes getText
        // which requires HttpContext.GetGlobalResourceObject
        // ... other stuff
    }
}

Note: these are simplistic examples.

The issue is that I get a Test Failed with the message:

Message: System.NullReferenceException : Object reference not set to an instance of an object.

With my sleuthing, I've determined that this is because HttpContext is null during these tests.

I've looked at quite a few SO posts on mocking HttpContext but I don't think that I fully understand what exactly they're doing as they're typically dealing with MVC and not Webforms. Still most of them use HttpContextBase and/or HttpContextWrapper but again, I'm not sure how to implement them.

Also - I'm not directly testing the getText method. I know it works. I'm testing a class that uses it. Will mocking the HttpContext even help in this situation?

I do realize that this is sort of a hybrid of a unit test / integration test, so if this isn't the best way, I'm all ears... or.. eyes rather.

Edit

For now, I modified my getText method to return the key (name) if the result of HttpContext.GetGlobalResourceObject is null. Then I updated my tests to expect the key instead of the value. It's not ideal, but it works and allows me to continue. If there's a better way, please let me know.

public static class MyStaticClass {
    public static string getText(String name)
    {
        String s = HttpContext.GetGlobalResourceObject("MyResources", name);
        return s != null ? s.ToString() : name;
    }
}

Answer 1

Original answer with Fakes (see below for dealing with removing static)

So there's one caveat that I completely forgot about until I just tried to do this. I am pretty sure Fakes still requires Enterprise version of VS. I don't know if there's a way to get it to work with NUnit, but when you aren't able to change the code sometimes you have to just deal with it.

Here's an example of Shimming your static method. You don't need to worry about HttpContext (yet) since you aren't using it directly. Instead you can Shim your getText(string) method.

Actual Business Project

namespace FakesExample
{
    public class MyStaticClass
    {
        public static string GetText(string name)
        {
            throw new NullReferenceException();
        }
    }
}

Your Unit Test Project

using System;
using Microsoft.QualityTools.Testing.Fakes;
using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace FakesExampleTests
{
    [TestClass]
    public class UnitTest1
    {
        [TestMethod]
        public void TestMethod1()
        {
            using (ShimsContext.Create())
            {
                FakesExample.Fakes.ShimMyStaticClass.GetTextString = (s) =>
                {
                    return "Go away null reference";
                };

                Console.WriteLine(FakesExample.MyStaticClass.GetText("foo"));
            }
        }
    }
}

I actually ran this so I know it works. What happens is that even though GetText will always throw a NullReferenceException when called, our Shim of it returns our own custom message.

You may have to make a Visual Studio Test Project.

In your Unit Test project, right-click your reference and say "Add Fakes". It will generate all of the Shims and Stubs for your assembly.

---

Process of removing the static

The best solution is to actually work towards removing the static. You've already hit one major reason to not use them.

Here's how I would go about removing the static and removing the dependency on HttpContext

public interface IResourceRepository
{
    string Get(string name);
}

public class HttpContextResourceRepository : IResourceRepository
{
    public string Get(string name)
    {
        return HttpContext.GetGlobalResourceObject("MyResources", name).ToString();
    }
}

public class MyFormerStaticClass
{
    IResourceRepository _resourceRepository;

    public MyFormerStaticClass(IResourceRepository resourceRepository)
    {
        _resourceRepository = resourceRepository;
    }

    public string GetText(string name)
    {
        return _resourceRepository.Get(name);
    }
}

I would then leverage Dependency Injection to handle the creation of my HttpContextResourceRepository and MyStaticClass (which should probably also be interfaced) in the actual business code.

For the unit test, I would mock the implementation

[TestFixture]
public class UnitTest1
{
    [Test]
    public void TestMethod1()
    {
        var repoMock = new Mock<IResourceRepository>();
        repoMock.Setup(repository => repository.Get("foo")).Returns("My Resource Value");

        var formerStatic = new MyFormerStaticClass(repoMock.Object);
        Console.WriteLine(formerStatic.GetText("foo"));
    }
}

Going this route, you can create any number of IResourceRepository implementations and swap them whenever you want.