Write Unit tests into an assembly or in a separate assembly?

Question

When writing unit tests, do you place your tests inside the assembly you wish to test or in a separate test assembly? I have written an application with the tests in classes

Answer 1

This is widely debated all over the net.

We use separate assemblies and the InternalsVisibleTo attribute to help the tester assemblies see all the innards of the tested assemblies. We tend to make one test assembly for each assembly we're testing.