Protection Levels and Visual Studio unit tests with C#

I am setting up some unit tests for a C# project I'm working on, and I opted to use Visual Studio's built-in unit test project. The problem is that I have been giving most of my classes in the project the default, `internal` access level. Now they can't be reached by my unit test project because it is a different assembly. It would be trivial to just make all my classes in the project `public` so that the unit test project can access them, but isn't it idiomatic to keep classes which are only used internally by a project `internal`?