How can I check in C# if a property of class is used in a Visual Studio solution?

I have a C# class with various static public properties which work as keys.

Through time, this class is refactored many times and some keys are deprecated and no longer are referenced from other classes from projects in the same Visual Studio solution.

I want with reflection or some other way to check if any of these keys (properties) are used in other classes in the Visual Studio solution.

I want to write a unit test to discover if any keys are not used any more.

How I could do such thing?