input: Write a function to count the frequency of each character in a given string and return the result as a dictionary.
  assert count_char_frequency("hello")=={'h': 1, 'e': 1, 'l': 2, 'o': 1}
  assert count_char_frequency("test")=={'t': 2, 'e': 1, 's': 1}
  assert count_char_frequency("aabbcc")=={'a': 2, 'b': 2, 'c': 2}
output: def count_char_frequency(s):
      freq = {}
      for char in s:
          if char in freq:
              freq[char] += 1
          else:
              freq[char] = 1
      return freq