Unit testing C# protected methods

Question

I come from the Java EE world but now I'm working on a .Net project. In Java when I wanted to test a protected method it was quite easy, just having the test class with the same package name was enough.

Is there anything similar for C#? Is there any good practice for unit testing the protected methods? I only found frameworks and people saying that I should test only public methods.

It should be possible to do it without any framework…

Answer 1

You can inherit the class you are testing on your test class.

[TestClass]
public class Test1 : SomeClass
{
    [TestMethod]
    public void MyTest
    {
        Assert.AreEqual(1, ProtectedMethod());
    }

}

Answer 2

You can expose the protected methods in a new class that inherits the class you want to test.

public class ExposedClassToTest : ClassToTest
{
    public bool ExposedProtectedMethod(int parameter)
    {
        return base.ProtectedMethod(parameter);
    }
}

Answer 3

Another option is to use internal for these methods and then use InternalsVisibleTo to allow your test assembly to access these methods. This does not stop the methods being consumed by other classes in the same assembly, but it does stop them being accessed by other assembles that are not your test assembly.

This does not give you as much encapsulation and protection but it's pretty straight forward and can be useful.

Add to AssemblyInfo.cs in the assembly containing the internal methods

[assembly: InternalsVisibleTo("TestsAssembly")]

Answer 4

You can use PrivateObject class to access all the private/ protected methods/ fields.

PrivateObject is a class in the Microsoft unit testing framework which is a wrapper that enables calling normally inaccessible members for unit testing.

Answer 5

You can use reflection to invoke private and protected methods.

See here for more:

http://msdn.microsoft.com/en-us/library/66btctbe.aspx

Answer 6

Although the accepted answer is the best one, it didn't solve my problem. Deriving from the protected class polluted my test class with a lot of other stuff. In the end I chose to extract the to-be-tested-logic into a public class and test that. Surely enough this will not work for everyone and might require quite some refactoring, but if you scrolled all the way up to this answer, it might just help you out. :) Here's an example

Old situation:

protected class ProtectedClass{
   protected void ProtectedMethod(){
      //logic you wanted to test but can't :(
   }
}

New situation:

protected class ProtectedClass{
   private INewPublicClass _newPublicClass;

   public ProtectedClass(INewPublicClass newPublicClass) {
      _newPublicClass = newPublicClass;
   }

   protected void ProtectedMethod(){
      //the logic you wanted to test has been moved to another class
      _newPublicClass.DoStuff();
   }
}

public class NewPublicClass : INewPublicClass
{
   public void DoStuff() {
      //this logic can be tested!
   }
}

public class NewPublicClassTest
{
    NewPublicClass _target;
    public void DoStuff_WithoutInput_ShouldSucceed() {
        //Arrange test and call the method with the logic you want to test
        _target.DoStuff();
    }
}

Answer 7

You can create a stub with a public method that calls the protected method from the base class. This is also how you would use this protected method in production.

public class FooStub : Bar 
{
    public string MyMethodFoo()
    {
        return MyMethodBar();
    }
}

public abstract class Bar 
{
    protected string MyMethodBar()
    {
        return "Hello World!"
    }
}

Answer 8

Here is the extension method (what is the extension method?) I am using in my testing project. The only downside is that you have to literally write the name as a string because nameof() follows the protection rules and does not allow you to refer to protected or private members.

        public static MethodInfo GetNonPublicMethod(this Type type, string method)
        {
            MemberInfo[] temp = type.GetMember(method, MemberTypes.Method, BindingFlags.NonPublic | BindingFlags.Instance);
            if (temp.Length == 1)
            {
                if (temp[0] is MethodInfo ret)
                {
                    return ret;
                }
                else
                {
                    throw new ArgumentException("Not a method.");
                }
            }
            else
            {
                if (temp.Length == 0)
                {
                    throw new ArgumentException("Method was not found.");
                }
                else
                {
                    throw new ArgumentException("Multiple methods found.");
                }
            }
        }

More on this method here: https://learn.microsoft.com/en-us/dotnet/api/system.type.getmember?view=net-5.0

PS: Use methodInfo.Invoke(instance, params) to call it.

Answer 9

Approach given in the first answer doesn't work and all protected methods are hidden. The base() should be added then protected methods will be visible.

[TestClass]
public class Test1 : SomeClass
{
    public Test1() : base()
    {
    }

    [TestMethod]
    public void MyTest
    {
        Assert.AreEqual(1, ProtectedMethod());
    }
}