Your solution passess all tests, so not a kata issue!

fixed

It's like Benjamin said, add this test to sample tests:

assert.equal( isIsogram("wrioacpuhZgzvdlmyfnb"), false , "It's a problem with your code");

You can see there are two zs there, the right answer is false, but your code returns true instead.

Fixed.

Hi, I don't use TypeScript but often this format of error message means "expected your answer to equal true answer "

In other words - again I'm not TypeScript user so I'm not 100% sure on the tests - it might be that your code is currently returning true.

To debug quickly: Check locally in your IDE for this particular input string, or include a "print" statement at the end of your code print_to_console : result (however you do this in your language) which will allow you to see what you are returning.

TypeScript

Which language?

One of random test, which wasn't passed - "ekdvikbp: expected true to equal false". How can be expected true, if 'k' is twice here?