That test is comparing the result of running your code to 26 and it is not so the test is failing. I suggest adding print statements to check what your code is returning.

Because of number of letters.
If you just sum ASCII numbers for each letter in a word "aa", you'll get "97 + 97" = "194", in the same time for word "w" you'll get "119", i.e. "194" > "119".
It's a wrong answer.
According to the task, you should consider letters position in the alphabet: a = 1, b = 2, c = 3 etc. : so you supposed to get for "aa" -> "1 + 1" ="2", and for "w" -> "23".
"23" > "2". The correct answer is "w".

The same doubt for me ...anyone explain this if you know the answer

Read stephane777's post below, it's been explained several times before. Tests are ok. You're not following the instructions.