Your solution has a bug, take a close look at the assetion message in test output panel. There is an invalid character between e and _. It's a result of an off-by-one error in your solution.

lol I can't see my own code because its marked spoiler and I haven;t submitted yet

Unfortuntely, yes.

ok, no worries :D

Uhhh actually I don't know why that is :D I can't really see what dotest is doing, and C++ is weird. It worked for me when I moved adding _ logic above, but I see solutions similar to yours, so IDK :/

lol I can't see my own code because its marked spoiler and I haven;t submitted yet

Try posting your code here as shown here and mark it as spoiler.

I don't think so, I don't use whitespace at all in the solution so don't know how that could happen.
'Actual' shows no whitespace too

Any trailing / leading whitespace?

I got the right answer, but it still failed me :(

odd_length
Expected: [ ab, cd, e_ ]
Actual: [ ab, cd, e_ ]