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>

diff --git a/src/errors/join_test.go b/src/errors/join_test.go
index 4828dc4d755fd678d0b3ca31f7fdebc5e1dcaeaf..8ee4d7f77be8856c1cd4d60fdafd2b5d0eb5cbff 100644 (file)
--- 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) {