What is the name of this unit-testing based method to learn coding?

A colleague of mine once showed me a way to practice programming for different languages. This method is based on empty test suites that the learner would fill. The tests cover different aspects of the language so that when you are done with the tests, you are supposed to have seen the most important features of the language.

This is a general concept, but I can't remember its name. And various searches in Google was of no help. Maybe someone will remember the name.

Thanks