Yet, this mutation is quite harmless for it adds an additional element and it doesn't actually modify any existing data. In that specific case, I would assume that adding data is actualy the requirement rather than not.

Thanks for pointing that out :)

bit of improvements =)

Maybe you should read the error message and the TDD box...

These tests are built in the system for users who want to make/customise their own testcases. You only have to pass the tests in the "Run Suite" section and not the "Run Examples" section (where the TDD is). If you want to make your own tests, you can put them in this box and click the "Run Examples" button, if you want to pass actual tests given by the author (allowing you to submit) then click the "Run Suite" button.

Run example not working, even with unlocked solution.

It gives an error:

should test for something
✘ This is just an example of how you can write your own TDD tests - Expected: "expected", instead got: "actual"