input: Write a function to identify the longest word in a given sentence. If the sentence contains multiple words of the same longest length, return the first one encountered.
  
  assert find_longest_word("The rain in Spain stays mainly in the plain.") == "mainly"
  assert find_longest_word("Python is a versatile programming language.") == "programming"
  assert find_longest_word("Short words like cat and dog.") == "words"
  assert find_longest_word("") == ""
  assert find_longest_word("A singlewordhere") == "singlewordhere"
output: def find_longest_word(sentence):
      words = sentence.split()
      if not words:
          return ""
      longest_word = words[0]
      for word in words:
          if len(word) > len(longest_word):
              longest_word = word
      return longest_word