arr = [1, 2, 3]
new_arr1 = pop(arr)
new_arr2 = pop(new_arr1)
new_arr3 = pop(new_arr2)
assert(new_arr1[0], isEqualTo = 1, error = "element 0 should not have changed")
assert(new_arr1[1], isEqualTo = 2, error = "element 1 should not have changed")
assert(new_arr2[0], isEqualTo = 1, error = "element 0 should not have changed")