input: Write a python function to count the occurrences of each word in a given string.
  assert word_count('This is a test string to count the words in the string.') == {'This': 1, 'is': 1, 'a': 1, 'test': 1, 'string': 2, 'to': 1, 'count': 1, 'the': 1, 'words': 1, 'in': 1}
  assert word_count('apple apple orange banana apple') == {'apple': 3, 'orange': 1, 'banana': 1}
  assert word_count('one two three two three three') == {'one': 1, 'two': 2, 'three': 3}
  assert word_count('repeat repeat repeat') == {'repeat': 3}
output: def word_count(s):
      words = s.split()
      count_dict = {}
      for word in words:
          count_dict[word] = count_dict.get(word, 0) + 1
      return count_dict