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.

1 files changed, 19 insertions, 3 deletions

diff --git a/django/test/runner.py b/django/test/runner.py
index ed969cc42f..aa2b269fab 100644
--- a/django/test/runner.py
+++ b/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):