From BlenderWiki

[edit] Automated Testing

Currently, Blender has no automatic testing. So far, most testing consists of rendering a set of 'test' .blend files manually, and checking the results. For the UI, testing is done manually by the developers and the community. Certainly, it is important to have manual testing, but at the same time, it is also very useful to have automated testing to quickly catch errors.

[edit] Unit Testing

Potential testing frameworks:

• CxxTest - Lightweight, simple, though hasn't been updated in quite some time.
• CppUnit - Probably too heavyweight.
• CuTest - Most lightweight of all; only a .h and a .c file. Tests run in the same process. I've used it before, it's simple.

[edit] Location of tests in blender tree

* source/test/
              track/          - camera track tests
              your-project/   - add your own tests
              sconstruct      - builds all the tests and runs them

[edit] Functional Testing

Functional testing is on hold until after the BlenderDev/EventSystemRefactoring, because then we can record logs and replay them to test functionality easily (this is hard/impossible now).