From 3faf988f217f59630509c057f48549f59a02c25e Mon Sep 17 00:00:00 2001
From: Damien Neil <dneil@google.com>
Date: Tue, 23 Dec 2025 09:42:37 -0800
Subject: [PATCH] errors: add a test verifying join does not flatten errors

For #76961

Change-Id: Ib81f3202074bf83a5b204b32706445f051f837a8
Reviewed-on: https://go-review.googlesource.com/c/go/+/732360
Auto-Submit: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Sean Liao <sean@liao.dev>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
---
 src/errors/join_test.go | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/errors/join_test.go b/src/errors/join_test.go
index 4828dc4d75..8ee4d7f77b 100644
--- a/src/errors/join_test.go
+++ b/src/errors/join_test.go
@@ -25,6 +25,7 @@ func TestJoinReturnsNil(t *testing.T) {
 func TestJoin(t *testing.T) {
 	err1 := errors.New("err1")
 	err2 := errors.New("err2")
+	merr := multiErr{errors.New("err3")}
 	for _, test := range []struct {
 		errs []error
 		want []error
@@ -37,6 +38,9 @@ func TestJoin(t *testing.T) {
 	}, {
 		errs: []error{err1, nil, err2},
 		want: []error{err1, err2},
+	}, {
+		errs: []error{merr},
+		want: []error{merr},
 	}} {
 		got := errors.Join(test.errs...).(interface{ Unwrap() []error }).Unwrap()
 		if !reflect.DeepEqual(got, test.want) {
-- 
2.52.0