C# "internal" access modifier when doing unit testing

[Clippy]

C# "internal" access modifier when doing unit testing

[Clippy]

Internal classes need to be tested and there is an assembly attribute:

```
using System.Runtime.CompilerServices;

[assembly:InternalsVisibleTo("MyTests")]

```

Add this to the project info file, e.g. `Properties\AssemblyInfo.cs`, for the project under test. In this case "MyTests" is the test project.