Fixed #33537 -- Made test database cloning on MySQL reraise unexpected errors.

Thanks Faakhir Zahid and Stephen Finucane for the initial patch.

Thanks Simon Charette for the review.

django/db/backends/mysql/creation.py

@@ -74,14 +74,27 @@ class DatabaseCreation(BaseDatabaseCreation):
         load_cmd = cmd_args
         load_cmd[-1] = target_database_name
 
-        with subprocess.Popen(
-            dump_cmd, stdout=subprocess.PIPE, env=dump_env
-        ) as dump_proc:
-            with subprocess.Popen(
+        with (
+            subprocess.Popen(
+                dump_cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, env=dump_env
+            ) as dump_proc,
+            subprocess.Popen(
                 load_cmd,
                 stdin=dump_proc.stdout,
                 stdout=subprocess.DEVNULL,
+                stderr=subprocess.PIPE,
                 env=load_env,
-            ):
-                # Allow dump_proc to receive a SIGPIPE if the load process exits.
-                dump_proc.stdout.close()
+            ) as load_proc,
+        ):
+            # Allow dump_proc to receive a SIGPIPE if the load process exits.
+            dump_proc.stdout.close()
+            dump_err = dump_proc.stderr.read().decode(errors="replace")
+            load_err = load_proc.stderr.read().decode(errors="replace")
+        if dump_proc.returncode != 0:
+            self.log(
+                f"Got an error on mysqldump when cloning the test database: {dump_err}"
+            )
+            sys.exit(dump_proc.returncode)
+        if load_proc.returncode != 0:
+            self.log(f"Got an error cloning the test database: {load_err}")
+            sys.exit(load_proc.returncode)

tests/backends/mysql/test_creation.py

@@ -1,12 +1,13 @@
 import subprocess
 import unittest
-from io import StringIO
+from io import BytesIO, StringIO
 from unittest import mock
 
 from django.db import DatabaseError, connection
 from django.db.backends.base.creation import BaseDatabaseCreation
 from django.db.backends.mysql.creation import DatabaseCreation
 from django.test import SimpleTestCase
+from django.test.utils import captured_stderr
 
 
 @unittest.skipUnless(connection.vendor == "mysql", "MySQL tests")
@@ -58,6 +59,8 @@ class DatabaseCreationTests(SimpleTestCase):
 
     def test_clone_test_db_options_ordering(self):
         creation = DatabaseCreation(connection)
+        mock_subprocess_call = mock.MagicMock()
+        mock_subprocess_call.returncode = 0
         try:
             saved_settings = connection.settings_dict
             connection.settings_dict = {
@@ -72,6 +75,7 @@ class DatabaseCreationTests(SimpleTestCase):
                 },
             }
             with mock.patch.object(subprocess, "Popen") as mocked_popen:
+                mocked_popen.return_value.__enter__.return_value = mock_subprocess_call
                 creation._clone_db("source_db", "target_db")
                 mocked_popen.assert_has_calls(
                     [
@@ -84,9 +88,51 @@ class DatabaseCreationTests(SimpleTestCase):
                                 "source_db",
                             ],
                             stdout=subprocess.PIPE,
+                            stderr=subprocess.PIPE,
                             env=None,
                         ),
                     ]
                 )
         finally:
             connection.settings_dict = saved_settings
+
+    def test_clone_test_db_subprocess_mysqldump_error(self):
+        creation = DatabaseCreation(connection)
+        mock_subprocess_call = mock.MagicMock()
+        mock_subprocess_call.returncode = 0
+        # Simulate mysqldump in test database cloning raises an error.
+        msg = "Couldn't execute 'SELECT ...'"
+        mock_subprocess_call_error = mock.MagicMock()
+        mock_subprocess_call_error.returncode = 2
+        mock_subprocess_call_error.stderr = BytesIO(msg.encode())
+        with mock.patch.object(subprocess, "Popen") as mocked_popen:
+            mocked_popen.return_value.__enter__.side_effect = [
+                mock_subprocess_call_error,  # mysqldump mock
+                mock_subprocess_call,  # load mock
+            ]
+            with captured_stderr() as err, self.assertRaises(SystemExit) as cm:
+                creation._clone_db("source_db", "target_db")
+            self.assertEqual(cm.exception.code, 2)
+        self.assertIn(
+            f"Got an error on mysqldump when cloning the test database: {msg}",
+            err.getvalue(),
+        )
+
+    def test_clone_test_db_subprocess_mysql_error(self):
+        creation = DatabaseCreation(connection)
+        mock_subprocess_call = mock.MagicMock()
+        mock_subprocess_call.returncode = 0
+        # Simulate load in test database cloning raises an error.
+        msg = "Some error"
+        mock_subprocess_call_error = mock.MagicMock()
+        mock_subprocess_call_error.returncode = 3
+        mock_subprocess_call_error.stderr = BytesIO(msg.encode())
+        with mock.patch.object(subprocess, "Popen") as mocked_popen:
+            mocked_popen.return_value.__enter__.side_effect = [
+                mock_subprocess_call,  # mysqldump mock
+                mock_subprocess_call_error,  # load mock
+            ]
+            with captured_stderr() as err, self.assertRaises(SystemExit) as cm:
+                creation._clone_db("source_db", "target_db")
+            self.assertEqual(cm.exception.code, 3)
+        self.assertIn(f"Got an error cloning the test database: {msg}", err.getvalue())