input: Write a function to take two lists as input and return a new list containing only the common elements. Use this assertion to test your function with the given output: 
  assert common_elements([1, 2, 3, 4, 8], [2, 6, 8, 10]) == [2, 8]
output: def common_elements(list1, list2):
      return list(set(list1) & set(list2))