The equal letters do not have to be adjacent.

abaa
bba
ca < order doesn't matter

expected 'abb' to equal 'ac' < this was the expected value
           ^             
 your code returned this 

given abaa |
Log |
abaa |
expected 'abb' to equal 'ac' |
.
A get 'ac'. Kata expects 'abb'? Shouldn't I convert two 'b'-s into on 'c'? I dont really understand.