From c9b61fc2a3d612485a60e5aa4e9c1d13fe1719ce Mon Sep 17 00:00:00 2001
From: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>
Date: Tue, 29 Sep 2026 17:25:32 +0100
Subject: [PATCH] Stop real threadpool for test DB pool before replacing it
 with threadless test implementation (#20272)

---
 changelog.d/20272.bugfix | 1 +
 tests/server.py          | 8 +++++++-
 2 files changed, 8 insertions(+), 1 deletion(-)
 create mode 100644 changelog.d/20272.bugfix

diff --git a/changelog.d/20272.bugfix b/changelog.d/20272.bugfix
new file mode 100644
index 0000000000..6b545eefcc
--- /dev/null
+++ b/changelog.d/20272.bugfix
@@ -0,0 +1 @@
+Prevent `trial` tests from hanging when running with Twisted 26.4.0 against Postgres.
\ No newline at end of file
diff --git a/tests/server.py b/tests/server.py
index 71f9da9c4c..3d44e11715 100644
--- a/tests/server.py
+++ b/tests/server.py
@@ -889,9 +889,15 @@ def make_fake_db_pool(
 
     pool.runWithConnection = runWithConnection  # type: ignore[method-assign]
     pool.runInteraction = runInteraction  # type: ignore[assignment]
-    # Replace the thread pool with a threadless 'thread' pool
+
+    # First, stop the original thread pool.
+    pool.threadpool.stop()
+    # Then, replace it with a threadless 'thread' pool
     pool.threadpool = ThreadPool(reactor)
+
+    # Start it up.
     pool.running = True
+
     return pool