Tests de preu_mig
-----------------

>>> import pandas as pd
>>> df = pd.read_csv('samarretes.csv')
>>> df.columns
Index(['Data', 'Comarca', 'Genere', 'Talla', 'Unitats', 'Preu unit.'], dtype='object')
>>> df.head(4)
         Data       Comarca Genere Talla  Unitats  Preu unit.
0  2000-10-10  Pla d'Urgell   home    XS        2        26.8
1  2000-12-04    Alt Urgell   dona     S       10        23.8
2  2000-01-09    Alt Urgell   dona    XL       13        23.9
3  2000-12-24     Baix Camp   dona   XXL        5        22.7

>>> from samarretes import preu_mig
>>> print(round(preu_mig(df, 'XS'), 2))
19.95
>>> print(round(preu_mig(df[300:], 'XXL'), 2))
19.99

>>> print(round(preu_mig(df, 'XXL'), 2))
19.68
>>> print(round(preu_mig(df[300:], 'XL'), 2))
20.79