I’ve found that while the tests help to know whether my code generally accomplishes the task, they’re not extensive enough to ensure my code meets all of the requirements of the problem. For example, there are no tests that ensure any edge cases are handled properly. In the solution review you mention that there could be duplicates of the same word in the input, but none of the tests check for that. My code assumed that there would not be duplicates and passed all of the tests.
I think it is good practice to write tests, so I’d love it if you open up the code a bit in the “Try it yourself” and I can do some blackbox test writing.