• Please show inputs on failing tests in assertion messages.
• Random test do not create cases with more than one unique character.

The setup does not enforce the use of a regex. Better way would be to let the user return a java.util.regex.Pattern object or even a pattern string and then use this to test passwords for validity.
Rejected.

Thanks! I corrected it

Description conflict.

Java translation provided

Java translation created

The test cases seem to be lacking. My original solution would fail if a letter appeared 3 times, yet it passed all the tests. I changed my solution and added the following tests for JavaScript, which failed with my original code.

Test.assertEquals(firstNonRepeatingLetter('abbaabczaz'), 'c');

Test.assertEquals(firstNonRepeatingLetter('zaazzapper'), 'e');

Test.assertEquals(firstNonRepeatingLetter('abbAabcZzaz'), 'c');

Test.assertEquals(firstNonRepeatingLetter('zaazzZxXAaaP3er'), 'P');