Question on self.subtest

Language Help Python
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1

Hello, I have a quick question on the usage of unittests, specifically, the subtest method.

in the Sam’s surf shop exercise project (https://www.codecademy.com/courses/learn-intermediate-python-3/projects/int-python-sams-surf-shop), step 10 tells us to parameterize a previous test.

# Write your code below:
import surfshop
import unittest

class SurfTest(unittest.TestCase):
  def setUp(self):
    self.cart = surfshop.ShoppingCart()

  
  def test_add_surfboards(self):
    for i in range(2,5):
      with self.subTest(i=i):
        test = self.cart.add_surfboards(i)
        self.assertEqual(test, f'Successfully added {i} surfboards to cart!')
        self.cart = surfshop.ShoppingCart()
                

  def test_add_surfboards_duo(self):
    test = self.cart.add_surfboards(2)
    self.assertEqual(test, 'Successfully added 2 surfboards to cart!')
  
  @unittest.skip
  def test_TooManyBoardsError(self):
    test = surfshop.TooManyBoardsError
    self.assertRaises(test, self.cart.add_surfboards, 5)
  
  @unittest.expectedFailure
  def test_discount(self):
    test = self.cart.apply_locals_discount()
    test
    self.assertTrue(self.cart.locals_discount)
  
unittest.main()

The last line on the test_add_surfboard function, it seems that if I don’t have it, the tests returns errors. Why is declaring:
self.cart = surfshop.ShoppingCart()

…a requirement for the test?

2

Hello!

I think we need to create a new instance of surfshop.ShoppingCart() in each subtest, because the setUp method is only executed before the test_* methods, but not before the subTest. So unless you create a new instance of ShoppingCart after completing the subtest, the number of surfboards in the cart will increase with each subtest, and you will get unexpected results.

2 Likes
3

So essentially, we don’t declare surfshop.ShoppingCart() for the other tests because those only iterates through the function once, meanwhile self.subTest() iterates through the function multiple times.

I’m just confused because I thought thats why we declared the setUp() method, because unittest.main() automatically refreshes each test so that the test environment is the same each time?