I am trying to work an F# tutorial on Pluralsight (see screencaps) where you have to install Xunit and write the tests but it's not working for me. It works fine for someone using Visual Studio as shown in the screencaps below, but I am not using Visual Studio. I'm on a Linux system using Monodevelop and I get this message: Composition error: the type 'Object' is required here and is unavailable. You must add a reference to assembly 'System.Runtime, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'
I think it must be the Assembly.fs file where I'm supposed to add the reference but I am not sure, nor do I know exactly how to add this reference correctly. Furthermore, I am unsure if the problem may be due to Monodevelop not recognizing a valid Linux path and if so, how to fix that. Any help would be greatly appreciated because I'm completely stuck.
Here is the error I'm getting in Monodevelop: