input: Write a python function to concatenate two lists.
  assert concatenateLists([1, 2, 3], [4, 5, 6]) == [1, 2, 3, 4, 5, 6]
  assert concatenateLists(['a', 'b'], ['c', 'd']) == ['a', 'b', 'c', 'd']
  assert concatenateLists([], [1, 2, 3]) == [1, 2, 3]
  assert concatenateLists([1, 2, 3], []) == [1, 2, 3]
output: def concatenateLists(list1, list2):
      return list1 + list2