input: Write a function to check if a string contains a given substring.
  assert checkIfStringContainsSubstring("hello world", "world") == True
  assert checkIfStringContainsSubstring("hello world", "WORLD") == False
  assert checkIfStringContainsSubstring("hello world", "hello") == True
  assert checkIfStringContainsSubstring("hello world", "test") == False
output: def checkIfStringContainsSubstring(string, substring):
      return substring in string