Make test less fragile and improve test name

The `test_returns_400_for_active_infractions_of_type_that_cannot_be_
active` test relied on the order in which the validation was done
since it contained incompatible combinations of arguments. The test
has been changed to make sure the data is valid except for the thing
we actually want to test.

I have also tried to improve the name of the test that tests the
`test_unique_constraint_accepts_active_infraction_after_inactive_
infraction` test. It now includes the logic of what it does, but
not the entire name of the test it's testing.

pydis_site/apps/api/tests/test_infractions.py

@@ -316,18 +316,22 @@ def test_returns_400_for_non_hidden_required_hidden_type(self):
     def test_returns_400_for_active_infraction_of_type_that_cannot_be_active(self):
         """Test if the API rejects active infractions for types that cannot be active."""
         url = reverse('bot:infraction-list', host='api')
-        restricted_types = ('note', 'warning', 'kick')
+        restricted_types = (
+            ('note', True),
+            ('warning', False),
+            ('kick', False),
+        )
 
-        for infraction_type in restricted_types:
+        for infraction_type, hidden in restricted_types:
             with self.subTest(infraction_type=infraction_type):
                 invalid_infraction = {
                     'user': self.user.id,
                     'actor': self.user.id,
                     'type': infraction_type,
                     'reason': 'Take me on!',
-                    'hidden': True,
+                    'hidden': hidden,
                     'active': True,
-                    'expires_at': '2019-10-04T12:52:00+00:00'
+                    'expires_at': None,
                 }
                 response = self.client.post(url, data=invalid_infraction)
                 self.assertEqual(response.status_code, 400)
@@ -450,7 +454,7 @@ def test_unique_constraint_accepts_active_infraction_after_inactive_infraction(s
             self.fail("An unexpected IntegrityError was raised.")
 
     @patch(f"{__name__}.Infraction")
-    def test_the_accepts_active_infraction_after_inactive_infractions_test(self, infraction_patch):
+    def test_if_accepts_active_infraction_test_catches_integrity_error(self, infraction_patch):
         """Does the test properly catch the IntegrityError and raise an AssertionError?"""
         infraction_patch.objects.create.side_effect = IntegrityError
         with self.assertRaises(AssertionError, msg="An unexpected IntegrityError was raised."):