Verrific

"Verrific" is an automated test framework for GameMaker. It's planned to support a wide range of testing scenarios and provide advanced tools for tests management.

...as of the current 0.1.0 version, it supports:

method-based unit test definitions basic value and type assertions wrappers for string and numeric fluent assertions It also provides a simple "log" runner that runs a given test suite, processes all its test and outputs the tests results along with their messages.