Unit Testing Private Methods in Unity Test Runner

Question

I'd like to do a unit test for my private methods in C#. Since the methods are private, they are not accessible from the test environment.

Answer 1

I figured out to do it this way:

1. Go to C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\Common7\IDE\PublicAssemblies\ and copy the file Microsoft.VisualStudio.QualityTools.UnitTestFramework.dll to a folder in your Unity project.
2. Reference the file in your .asmdef file, which you find in the "Tests" folder:
3. In your c# test script, you now can access this adding using Microsoft.VisualStudio.TestTools.UnitTesting;
4. Instantiate an instance of your class containing the method to test and create a private object as well. In case the method you want to test is static, create a private type instead:

    public class MyClass
    {
        private static int AddOne(int i)
        {
            return i += 1;
        }
        private int SubOne(int i)
        {
            return i -= 1;
        }
    }

    MyClass myClass = new MyClass();
    PrivateType privateTypeMyClass = new PrivateType(myClass.GetType());
    int res1 = (int)privateTypeMyClass .InvokeStatic("AddOne", 2);
    PrivateObject privateObjectMyClass = new PrivateObject(myClass);
    int res2 = (int)privateObjectMyClass.Invoke("AddOne", 2);

5. If you want to pass more than one argument, you can use an obj[] to pass these.

Answer 2

It is not suggested to write unit tests for private methods. You should write tests only and only for the public methods because a caller interacts with your class only through public methods and properties. In the flow, private methods get called by the public methods. So write your tests such that they call the public methods and covers private methods via different flows. This way you will also be able to know if there are some unused private methods in your code which can be deleted.