input: Write a function to find the union of two lists and return a set containing all unique elements from both lists.
  
  def unionList(list1, list2):
      return set(list1 + list2)
  
  assert unionList([1, 2, 3, 4, 5], [3, 4, 5, 6, 7])=={1, 2, 3, 4, 5, 6, 7}
  assert unionList([], [1, 2, 3])=={1, 2, 3}
  assert unionList([5, 6, 7], [1, 2, 3])=={1, 2, 3, 5, 6, 7}
  assert unionList([], [])==set()
  assert unionList([1, 2, 3], [4, 5, 6])=={1, 2, 3, 4, 5, 6}
output: def unionList(list1, list2):
      return set(list1 + list2)