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