Visual Studio Community unit testing (c++)

I wanted to add unit tests to a software-project in Visual Studio Community.

I right-clicked on my project folder and created a new test project. Then I right clicked on my new Test Project and added a reference to my c++ project. How can I reference my source code in my test project?

The problem is, that I can't include anything from my c++ project (and therefore can't test anything from my code).

As I am new to C++: Are there any other plugins/extensions for unit testing you can recommend?

Many thanks in advance,