import os
import unittest
from importlib import import_module

invoice_total = import_module(os.environ.get("INVOICE_MODULE", "invoice_buggy")).invoice_total


class InvoiceTotalTests(unittest.TestCase):
    def test_distinct_items(self):
        self.assertEqual(invoice_total([1250, 750]), 2000)

    def test_equal_prices_are_separate_line_items(self):
        self.assertEqual(invoice_total([1250, 1250]), 2500)

    def test_empty_invoice(self):
        self.assertEqual(invoice_total([]), 0)


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