so MoOse and moose would be treated the same way

Test for "moose" expects false. Test for "moOse" expects false. Relevant assertions in tests are:

assert.strictEqual( isIsogram("moose"), false );
assert.strictEqual( isIsogram("moOse"), false, "same chars may not be same case" );

Doesn't this mean they both behave the same way? What is different about them?

The tests expects false, I don't know what you're complaining about, the test is fine, you're wrong.

assert.equal( isIsogram("moOse"), false, "same chars may not be same case" );

That is the test, if it would be case-sensitive as you claim, it would expect true because o and O would be considered different letters, but it isn't.

Please read the definition of case insensitive here: https://en.wikipedia.org/wiki/Case_sensitivity

In case-insensitive, uppercase and lowercase letters are the same, and that's what the test asks.

I would appreciate some explanation from you why you consider my answers wrong, and what is the error in tests you are complaining about, because I think I am missing something:

• The word moose is not an isogram, because the letter o occurs twice.
• The word mOose is not an isogram, because the letter o occurs twice, with differend case (lowercase and uppercase).

The occurrence of letters should be done in a case-insensitive way, i.e. both lowercase letters and uppercase letters contribute to the count of occurrences. And this is how it works in JavaScript translation. So, what exactly you think is wrong?

I'm not sure if I should be proud of it to be honest... but I can't take it back now