Lecture 13, Wed 09/06

import pytest

def countAs(s):
   " count a and A in string s "
   if type(s)!=str:
      raise ValueError('parameter to countAs should be of type str')
   count = 0
   for c in s:
      if c=='a' or c=='A':
         count = count + 1
   return count


def test_countAs_1():
    with pytest.raises(ValueError):
       result = countAs(-42)
       
def test_countAs_2():
   assert countAs("Santa Ana")==4