Although this is an old comment I will respond for any future coders.

Take care to notice that there are two spaces (" ") in the test case and that is the reason the test should fail. Not because of the "Aa"

typo. I changed that, thx.

Hi.

Why the instructions says you can use the scale twice but a commentary in code says that you can use max 4 times?

Thanks for your answer.

The following test make my thought that solution must be non case-sensitive:
Test.assertEquals(hasUniqueChars(" nAa"),false)
But the tests when I submit my solution take care about that so check please.