input: Write a python function to count the occurrences of each character in a string.
  assert countCharacters("hello")=={'h': 1, 'e': 1, 'l': 2, 'o': 1}
  assert countCharacters("test")=={'t': 2, 'e': 1, 's': 1}
  assert countCharacters("abcabc")=={'a': 2, 'b': 2, 'c': 2}
output: def countCharacters(s):
      char_count = {}
      for char in s:
          if char in char_count:
              char_count[char] += 1
          else:
              char_count[char] = 1
      return char_count