import unittest
from checkout.service import calculate_checkout

class BaselineCheckoutTests(unittest.TestCase):
    def test_no_coupon(self):
        self.assertEqual(calculate_checkout(100.0, None).total, 108.0)

    def test_coupon_above_threshold(self):
        self.assertEqual(calculate_checkout(120.0, "SAVE10").total, 116.64)

    def test_coupon_below_threshold_is_not_applied(self):
        self.assertEqual(calculate_checkout(99.0, "SAVE10").total, 106.92)

if __name__ == '__main__':
    unittest.main()