input: Write a python function to check if two strings are equal.
  assert check_strings_equal("test", "test") == True
  assert check_strings_equal("hello", "world") == False
  assert check_strings_equal("python", "python") == True
  assert check_strings_equal("OpenAI", "openai") == False
output: def check_strings_equal(str1, str2):
      return str1 == str2