I'm not the original poster, but I seem to have the same issue. My code does pass the example, and if on the actual solution I return something like str+" " (adding an extra space to make it wrong) it will say I failed 2 tests and will show me the results (for which my output seems to match expected result, with the exception of the space).

If the solution should be correct though, it says 0 failed, 0 passed, has a red border, but green arrows for fixed test, but doesn't show expected vs actual results nor random test header. Also the ms time is quite low vs when it's incorrect from adding a space. This seems to suggest (at a guess) if it passes the fixed test, it stops without trying the random test for some reason.

I did some benchmarking using node for ~10 of the higher rated solutions on this problem currently, this one and the one by SupraDeus would seem to run by far the fastest of those I checked (this one is seemingly a bit faster for smaller spirals, and a bit slower on larger ones compared to SupraDeus's based on my limited tests).

Anyways, food for thought.