Make method only callable from unit test

Question

Is it possible to write methods, which are only callable by unit tests? My problem is that our framework contains a lot of Singleton classes, which makes unit testing quite hard some time. My idea was to create a simple interface like this:

public interface IUnitTestClearable
{
    void ClearForUnitTest();
}

This method will be called for "resetting" singleton instances for better handling of unit tests. But this method should only be callable from unit test classes/instances. Is this possible?

Answer 1

You can make a method internal and then set InternalsVisibleTo. This way, you give another assembly access to your internals

http://geekswithblogs.net/jwhitehorn/archive/2007/11/09/116750.aspx

but Tim was just before me as I end this :)

In your project file, AssemblyInfo.cs, set

[assembly: InternalsVisibleTo("Application.Test")]

or if you have a signed assembly

[assembly: InternalsVisibleTo("Application.Test, PublicKey=KEYHERE")]

Answer 2

Providing access to unit tests while controlling or preventing other things (ab)using that access is a good idea. There are a number of ways this can be done but the simplest is to use InternalsVisibleTo

https://docs.microsoft.com/en-us/dotnet/api/system.runtime.compilerservices.internalsvisibletoattribute

Answer 3

You may not want to expose all private methods to your unit tests, as it might cause confusion, so just add a private method for your singleton classes.

public class MySingleton
{
    private void ClearForUnitTest()
    {
        Console.WriteLine("Cleared.");
    }
}

Create extension to be used in your unit tests.

public static class PrivateExtensions
{
    public static void ClearForUnitTest<T>(this T instance)
    {
        var method = typeof(T).GetMethod("ClearForUnitTest", BindingFlags.NonPublic | BindingFlags.Instance);
        method.Invoke(instance, null);
    }
}

Use like it would be public

private static void Main(string[] args)
{
    var ms = new MySingleton();
    ms.ClearForUnitTest();
}

profit