I wrote code which correctly produced diamonds, but the test kept failing because apparently my diamond wasn't the same as the desired diamonds. The 'expected' and 'actual' output seemed exactly the same and it took me over an hour to figure out the difference; the test expects a newline appended at the end of diamonds.

This shouldn't be a requirement. It's not listed in the requirements and the tests don't really show this either. I wasted an hour tracking this
down. I want my hour back.

It doesn't help that the 'actual' test output always has a space character prepended, further confusing me/the programmer.