Specify behaviour in TransactionTestCase.reset_sequences

[Slava M.]

​https://docs.djangoproject.com/en/dev/topics/testing/advanced/#django.test.TransactionTestCase.reset_sequences

I suggest specifying behaviour of TransactionTestCase.reset_sequences when used in subtests ​https://docs.python.org/3/library/unittest.html#distinguishing-test-iterations-using-subtests.

i.e.

class TestsThatDependsOnPrimaryKeySequences(TransactionTestCase):
    reset_sequences = True

    def test_animal_pk(self):
        with self.subTest():
            lion = Animal.objects.create(name="lion", sound="roar")
            self.assertEqual(lion.pk, 1)
        with self.subTest():
            cat = Animal.objects.create(name="cat", sound="meow")
            # will this still work?
            self.assertEqual(cat.pk, 1)

add to documentation 1 sentence along the lines of:

• "reset_sequences won't work with unittest's subTest()"
• or ""reset_sequences also works with unittest's subTest()"

[Simon Charette]

If we are to add a note about subTest, I'm not entirely convinced it's needed, I believe we should only focus on the behavior of reset_sequences but all the database isolation features that TransactionTestCase and TestCase does provide within the context of distinct test_ method. In other words, no per subTest data isolation (sequence, transactions, mailbox, etc) is implemented and within the context of a TransactionTestCase and friends a subTest context is solely a manner to annotate part of a test case method body with some context.

[Sarah Boyce]

Replying to Simon Charette:

...a subTest context is solely a manner to annotate part of a test case method body with some context.

Exactly - subTest is a ​unittest feature, not a Django feature, and any setUp() or tearDown() etc happens per test (not per subTest). The reset_sequences behavior is consistent to this. Hence, I don't think we need to add documentation to Django on this