The new `test_blackjack.py`

file looks like this;

```
from blackjack import card_score
def test_simple_usecase1():
card_score("JK") == 20
def test_simple_usecase2():
card_score("JKQ") == 0
def test_simple_usecase3():
card_score("KA") == 21
def test_simple_usecase4():
card_score("AA") == 12
```

And the fixed function looks like this;

```
def card_score(cards):
numbers = [c for c in cards if c in "23456789"]
faces = [c for c in cards if c in "JQK"]
n_aces = sum([1 for c in cards if c == "A"])
score = sum([int(i) for i in numbers]) + len(faces) * 10
while n_aces > 0:
score += 1 if score + 11 > 21 else 11
n_aces -= 1
return score if score <= 21 else 0
```