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