Can't access C# Script classes in Unity Test Framework (Unity 2020.2.0b7)

I have a static C# class that I want to test but I'm having trouble accessing the class in my test files.
I'm getting the error: The name 'SampleClass' does not exist in the current context [Tests]csharp(CS0103)
Here is what I have done so far.

1. Create "EditMode" `Tests.asmdef` file in `Tests` directory
2. Create `GameAssembly` Assembly Definition in my `Scripts` directory
3. Add the `GameAssembly` to Assembly Definition References list in Tests.asmdef.

Is there something I'm missing?

My test file:

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using NUnit.Framework;
4. using UnityEngine;
5. using UnityEngine.TestTools;
6.  
7. public class SampleClassTest
8. {
9.     // A Test behaves as an ordinary method
10.     [Test]
11.     public void AddTest()
12.     {
13.         int result = SampleClass.Add(1, 1);
14.         Assert.AreEqual(2, result);
15.     }
16. }
17.  

Tests Assembly config:


GameAssembly config:

 

So where exactly is SampleClass defined?

 

It's defined in Assets/Scripts/ directory