How to Separate Unit Test and Integration Tests

So often I see unit test and integration tests mixed. What is the correct way to keep those things separate? Some projects internally at Microsoft right now where the argument about unit testing versus integration testing is happening. We're all using unit testing tools for both unit testing and integration. That blurs things for new people. But seriously, just so on the human factor, it's easier to run all the tests in the project than all the Tests in the namespace or folder. It's easier. So you want to make things easier for people and they will do them.