This is not correct.  The use of `RootDirectory` here is required.

See any game sample...

https://github.com/Mono-Game/MonoGame.Samples/blob/master/Platformer2D/Game.cs#L62

... the RootDirectory is the folder where your content is stored.  It normally isn't an absolute path itself.

That said the testing framework runs under Microsoft XNA as well as MonoGame.  If the test framework is setting an absolute path on `ContentManager.RootDirectory` and that works under XNA then we're missing something in our implementation.