old_contents: from usernames import is_safe_username
  
  
  def test_usernames():
      unsafe_words = [
          '!',
          '#',
          '',
          '()',
          '-hello',
          '.hello',
          'fuck',
          'hel--lo',
          'hel-.lo',
          'hel..lo',
          'hel__lo',
          'hello-',
          'hello.',
          'sex',
      ]
  
      safe_words = [
          '10101',
          '1he-llo',
          '_hello',
          'he-llo',
          'he.llo_',
          'hello',
          'hello_',
      ]
  
      for w in unsafe_words:
          assert not is_safe_username(w)
  
      for w in safe_words:
          assert is_safe_username(w)
  
new_contents: from usernames import is_safe_username
  
  
  def test_usernames():
      unsafe_words = [
          '!',
          '#',
          '',
          '()',
          '-',
          '-hello',
          '.',
          '.hello',
          '_',
          'fuck',
          'hel--lo',
          'hel-.lo',
          'hel..lo',
          'hel__lo',
          'hello-',
          'hello.',
          'sex',
      ]
  
      safe_words = [
          'a'
          '10101',
          '1he-llo',
          '_hello',
          'he-llo',
          'he.llo_',
          'hello',
          'hello_',
      ]
  
      for w in unsafe_words:
          assert not is_safe_username(w)
  
      for w in safe_words:
          assert is_safe_username(w)
  
subject: Add more test samples