From 4dbb3a236cb7a02e72d55dfe72587eba27df5814 Mon Sep 17 00:00:00 2001
From: Ethan <39577870+ethanndickson@users.noreply.github.com>
Date: Tue, 4 Aug 2026 01:03:30 +1000
Subject: [PATCH] test: fix tailnet connection teardown flake (#27768)

Closes https://github.com/coder/internal/issues/1620
Closes ENG-3043

The callback cleanup added in #20687 stops new node callbacks, but it
can still race with one that's already in flight. That callback may call
`UpdatePeers` after the destination `tailnet.Conn` closes, so the test
fails with `connection closed` even though the redirect behaviour is
correct.

To fix, we'll just ignore `tailnet.ErrConnClosed` in the asynchronous
`stitch` helpers, whilst continuing to assert on every other error.
---
 codersdk/workspacesdk/agentconn_test.go | 4 +++-
 tailnet/conn_test.go                    | 5 ++++-
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/codersdk/workspacesdk/agentconn_test.go b/codersdk/workspacesdk/agentconn_test.go
index c77cbae3ce..a2cce9d5cd 100644
--- a/codersdk/workspacesdk/agentconn_test.go
+++ b/codersdk/workspacesdk/agentconn_test.go
@@ -243,7 +243,9 @@ func stitchTailnet(t *testing.T, conns map[uuid.UUID]*tailnet.Conn) {
 				Node: protoNode,
 				Kind: proto.CoordinateResponse_PeerUpdate_NODE,
 			}})
-			assert.NoError(t, err)
+			if err != nil && !errors.Is(err, tailnet.ErrConnClosed) {
+				assert.NoError(t, err)
+			}
 		}
 	}
 
diff --git a/tailnet/conn_test.go b/tailnet/conn_test.go
index 7e8ac53474..b2c9cd575e 100644
--- a/tailnet/conn_test.go
+++ b/tailnet/conn_test.go
@@ -2,6 +2,7 @@ package tailnet_test
 
 import (
 	"context"
+	"errors"
 	"net"
 	"net/netip"
 	"strings"
@@ -483,7 +484,9 @@ func stitch(t *testing.T, dst, src *tailnet.Conn) {
 			Node: pn,
 			Kind: proto.CoordinateResponse_PeerUpdate_NODE,
 		}})
-		assert.NoError(t, err)
+		if err != nil && !errors.Is(err, tailnet.ErrConnClosed) {
+			assert.NoError(t, err)
+		}
 	})
 	// ensures we don't send callbacks after the test ends and connections are closed.
 	t.Cleanup(func() {