input: Write a function to identify the longest word in a given sentence. The function should return the longest word found in the sentence. If there are multiple words with the same longest length, return the first one encountered.
  def find_longest_word(sentence):
      words = sentence.split()
      # initialise longest_word variable with 0
      longest_word = 0
      for word in words:
          if len(word) > longest_word:
              longest_word = len(word)
              longest_word_str = word
      return longest_word_str
  assert find_longest_word("The rain in Spain stays mainly in the plain.") == "mainly"
  assert find_longest_word("This is a test sentence.") == "sentence"
  assert find_longest_word("Python is awesome.") == "Python"
  assert find_longest_word("Singleword") == "Singleword"
  assert find_longest_word("") == ""
output: def find_longest_word(sentence):
      words = sentence.split()
      longest_word = ""
      for word in words:
          if len(word) > len(longest_word):
              longest_word = word
      return longest_word