Zephyr writing tests

I read the documentation here: http://ift.tt/1MS4nbB

about writing tests in zephyr, but I'm not sure what those tests are supposed to entail.

For example, that video shows one test case as "Verify app can be installed from store" or something similar to that.

But what does the test actually consist of? Is it code? Can you write Java JUnit tests in there?

What are you actually testing?

Thanks