Remove duplicates in Order

Write a function remove_duplicates_in_order that receives a list and returns a new list with the duplicates elements removed.
Important! The elements should be in order. Example:

remove_duplicates_in_order([2,1,1,3,4], [2,1,3,4])
import unittest


class RemoveDuplicatesTestCase(unittest.TestCase):
    def test_remove_duplicates_in_order(self):
        self.assertEqual(remove_duplicates_in_order([2,1,1,3,4]), [2,1,3,4])

    def test_remove_duplicates_in_order_with_empty_list(self):
        self.assertEqual(remove_duplicates_in_order([]), [])