Unclear that tests actually validate their results?

https://github.com/firebase/snippets-web/blob/c5bfca32e881d7a40002285384a784749f973c35/firestore/test.solution-counters.js#L49

In the test group that starts at the above line, it isn't clear to me that the results of the tests are actually being tested? What validates that the counters are created? What validates that the incremented value is correct?