Next Chapter 5. Most regression testing as done by DejaGnu is system testing. This is the complete application is tested all at once.
Unit testing is for testing single files, or small libraries.
This works particularly well for testing APIs and at level where it is easier to debug them, than by needing to trace through the entire appication. Also if there is a specification for the API to be tested, the testcase can also function as a compliance test. Next Special variables used by test cases.