Fixed #25251 -- Made data migrations available in TransactionTestCase when using --keepdb.

Data loaded in migrations were restored at the beginning of each
TransactionTestCase and all the tables are truncated at the end of
these test cases. If there was a TransactionTestCase at the end of
the test suite, the migrated data weren't restored in the database
(especially unexpected when using --keepdb). Now data is restored
at the end of each TransactionTestCase.

django/test/runner.py

@@ -11,7 +11,7 @@ from io import StringIO
 
 from django.core.management import call_command
 from django.db import connections
-from django.test import SimpleTestCase, TestCase
+from django.test import SimpleTestCase, TestCase, TransactionTestCase
 from django.test.utils import (
     setup_databases as _setup_databases, setup_test_environment,
     teardown_databases as _teardown_databases, teardown_test_environment,
@@ -399,7 +399,7 @@ class DiscoverRunner:
     parallel_test_suite = ParallelTestSuite
     test_runner = unittest.TextTestRunner
     test_loader = unittest.defaultTestLoader
-    reorder_by = (TestCase, SimpleTestCase)
+    reorder_by = (TestCase, TransactionTestCase, SimpleTestCase)
 
     def __init__(self, pattern=None, top_level=None, verbosity=1,
                  interactive=True, failfast=False, keepdb=False,
@@ -637,6 +637,22 @@ def is_discoverable(label):
     return os.path.isdir(os.path.abspath(label))
 
 
+def reorder_postprocess(reordered_suite):
+    """
+    To make TransactionTestCases initialize their data properly, they must know
+    if the next TransactionTestCase needs initial data migrations serialized in
+    the connection. Initialize _next_serialized_rollback attribute depending on
+    the serialized_rollback option present in the next test class in the suite.
+    If the next test has no serialized_rollback attribute, it means there
+    aren't any more TransactionTestCases.
+    """
+    for previous_test, next_test in zip(reordered_suite._tests[:-1], reordered_suite._tests[1:]):
+        next_serialized_rollback = getattr(next_test, 'serialized_rollback', None)
+        if next_serialized_rollback is not None:
+            previous_test._next_serialized_rollback = next_serialized_rollback
+    return reordered_suite
+
+
 def reorder_suite(suite, classes, reverse=False):
     """
     Reorder a test suite by test type.
@@ -656,7 +672,7 @@ def reorder_suite(suite, classes, reverse=False):
     reordered_suite = suite_class()
     for i in range(class_count + 1):
         reordered_suite.addTests(bins[i])
-    return reordered_suite
+    return reorder_postprocess(reordered_suite)
 
 
 def partition_suite_by_type(suite, classes, bins, reverse=False):

django/test/testcases.py

@@ -827,6 +827,15 @@ class TransactionTestCase(SimpleTestCase):
     # This can be slow; this flag allows enabling on a per-case basis.
     serialized_rollback = False
 
+    # This attribute is strongly linked to serialized_rollback parameter and
+    # allows the data restoration after the database flush, at the end of the
+    # test, if the next test needs the initial data. This attribute is updated
+    # by the test runner when the test suite is built. Being initialized to
+    # True is crucial: the last TransactionTestCase, which doesn't have any
+    # test classes with the serialized_rollback attribute, will always have
+    # this value set to True.
+    _next_serialized_rollback = True
+
     # Since tests will be wrapped in a transaction, or serialized if they
     # are not available, we allow queries to be run.
     allow_database_queries = True
@@ -897,17 +906,6 @@ class TransactionTestCase(SimpleTestCase):
             if self.reset_sequences:
                 self._reset_sequences(db_name)
 
-            # If we need to provide replica initial data from migrated apps,
-            # then do so.
-            if self.serialized_rollback and hasattr(connections[db_name], "_test_serialized_contents"):
-                if self.available_apps is not None:
-                    apps.unset_available_apps()
-                connections[db_name].creation.deserialize_db_from_string(
-                    connections[db_name]._test_serialized_contents
-                )
-                if self.available_apps is not None:
-                    apps.set_available_apps(self.available_apps)
-
             if self.fixtures:
                 # We have to use this slightly awkward syntax due to the fact
                 # that we're using *args and **kwargs together.
@@ -961,6 +959,15 @@ class TransactionTestCase(SimpleTestCase):
                          database=db_name, reset_sequences=False,
                          allow_cascade=self.available_apps is not None,
                          inhibit_post_migrate=inhibit_post_migrate)
+            # Provide replica initial data from migrated apps, if needed.
+            if self._next_serialized_rollback and hasattr(connections[db_name], '_test_serialized_contents'):
+                if self.available_apps is not None:
+                    apps.unset_available_apps()
+                connections[db_name].creation.deserialize_db_from_string(
+                    connections[db_name]._test_serialized_contents
+                )
+                if self.available_apps is not None:
+                    apps.set_available_apps(self.available_apps)
 
     def assertQuerysetEqual(self, qs, values, transform=repr, ordered=True, msg=None):
         items = map(transform, qs)