Condition to count could be made better for performance. Performance is going to be better simply by comparing every char in input string against a set of vowels.

Simple and also readable compared to other solutions.

Why is this 7kyu? Should be 8kyu.

Nice explanation for identity.

added a broken initial solution

I'm getting the same message. One assert is expecting my function to return an empty string if all categories are 0, but another one is expecting the regular "(B : 0) - ..."
(This is in C++)
If this is intended, then I am smol brain...
Update: Okay, I read the last line in your instructions...

This should be fixed.

I am afraid there is nothing to fix. I tried some solutions, they worked fine and 90 people passed the Scala translation.
Anyway you should give the inputs.

Scala testcases have contradicting testcases due to which submissions are failing.

Test Failed
Expected "[]", but got "[(B : 0) - (R : 0) - (D : 0) - (X : 0)]"

Test Failed
Expected "[(A : 0) - (W : 0) - (D : 0) - (C : 0) - (X : 0)]", but got "[]"

This should be fixed.

This should be a 7kyu IMO.

From learning point of view, I learnt about comparison op with string but from readability point of view, the solution left me ambigous about why explicit conversion to Integer is not implememted.

scala.collection.immutable.StringOps, conversions in scala.Predef.

Was not aware filter can be applied on String in Scala because getClass() only returns java.lang.String. There is filter() method in java.lang.String class. What is the class to look for the documentaion scala string (if there is something like that)?
val s = "hello"
println(s.getClass())