test: add test to reproduce the double header write issue

1 files changed, 36 insertions, 1 deletions

diff --git a/app/controllers/sparkles/controller_test.go b/app/controllers/sparkles/controller_test.go
index 0619b99..37e1a82 100644
--- a/app/controllers/sparkles/controller_test.go
+++ b/app/controllers/sparkles/controller_test.go
@@ -1,7 +1,9 @@
 package sparkles
 
 import (
+	"errors"
 	"net/http"
+	"net/http/httptest"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -13,6 +15,22 @@ import (
 	"gitlab.com/gitlab-org/software-supply-chain-security/authorization/sparkled/app/domain"
 )
 
+type FailingResponseWriter struct {
+	*testing.T
+	*httptest.ResponseRecorder
+	headerWritten bool
+}
+
+func (f *FailingResponseWriter) WriteHeader(statusCode int) {
+	require.False(f.T, f.headerWritten)
+	f.headerWritten = true
+	f.ResponseRecorder.WriteHeader(statusCode)
+}
+
+func (f *FailingResponseWriter) Write([]byte) (int, error) {
+	return 0, errors.New("write failed")
+}
+
 func TestSparkles(t *testing.T) {
 	t.Run("GET /sparkles", func(t *testing.T) {
 		sparkle, _ := domain.NewSparkle("@tanuki for helping me")
@@ -47,7 +65,6 @@ func TestSparkles(t *testing.T) {
 			currentUser := domain.NewUser(domain.WithID[*domain.User](domain.ID("1")))
 
 			t.Run("saves a new sparkle", func(t *testing.T) {
-
 				repository := db.NewRepository[*domain.Sparkle]()
 				mux := http.NewServeMux()
 				controller := New(repository)
@@ -84,6 +101,24 @@ func TestSparkles(t *testing.T) {
 					assert.Equal(t, currentUser, item.Author)
 				})
 			})
+
+			t.Run("prevents double WriteHeader when serialization fails", func(t *testing.T) {
+				repository := db.NewRepository[*domain.Sparkle]()
+				controller := New(repository)
+
+				currentUser := domain.NewUser(domain.WithID[*domain.User](domain.ID("1")))
+				sparkle, _ := domain.NewSparkle("@user for testing")
+
+				request, response := test.RequestResponse(
+					"POST",
+					"/sparkles",
+					test.WithAcceptHeader(serde.JSON),
+					test.WithContentType(sparkle, serde.JSON),
+					test.WithContextKeyValue(t.Context(), cfg.CurrentUser, currentUser),
+				)
+
+				controller.Create(&FailingResponseWriter{T: t, ResponseRecorder: response}, request)
+			})
 		})
 	})
 }