input: Write a function to create a dictionary that maps each word to its occurrence from a given text.
  assert word_count("Hello world! Hello everyone.") == {'hello': 2, 'world!': 1, 'everyone.': 1}
  assert word_count("This is a test. This test is only a test.") == {'this': 2, 'is': 2, 'a': 2, 'test.': 2, 'only': 1}
  assert word_count("One fish, two fish, red fish, blue fish.") == {'one': 1, 'fish,': 4, 'two': 1, 'red': 1, 'blue': 1}
output: def word_count(text):
      words = text.lower().split()
      word_dict = {}
      for word in words:
          if word in word_dict:
              word_dict[word] += 1
          else:
              word_dict[word] = 1
      return word_dict