improve render code coverage (#3525)

Author: CCpro10

render/render_test.go

@@ -15,6 +15,7 @@ import (
 "strings"
 "testing"
 
+"github.com/gin-gonic/gin/internal/json"
 testdata "github.com/gin-gonic/gin/testdata/protoexample"
 "github.com/stretchr/testify/assert"
 "google.golang.org/protobuf/proto"
@@ -136,6 +137,51 @@ func TestRenderJsonpJSON(t *testing.T) {
 assert.Equal(t, "application/javascript; charset=utf-8", w2.Header().Get("Content-Type"))
 }
 
+type errorWriter struct {
+bufString string
+*httptest.ResponseRecorder
+}
+
+var _ http.ResponseWriter = (*errorWriter)(nil)
+
+func (w *errorWriter) Write(buf []byte) (int, error) {
+if string(buf) == w.bufString {
+return 0, errors.New(`write "` + w.bufString + `" error`)
+}
+return w.ResponseRecorder.Write(buf)
+}
+
+func TestRenderJsonpJSONError(t *testing.T) {
+ew := &errorWriter{
+ResponseRecorder: httptest.NewRecorder(),
+}
+
+jsonpJSON := JsonpJSON{
+Callback: "foo",
+Data: map[string]string{
+"foo": "bar",
+},
+}
+
+cb := template.JSEscapeString(jsonpJSON.Callback)
+ew.bufString = cb
+err := jsonpJSON.Render(ew) // error was returned while writing callback
+assert.Equal(t, `write "`+cb+`" error`, err.Error())
+
+ew.bufString = `(`
+err = jsonpJSON.Render(ew)
+assert.Equal(t, `write "`+`(`+`" error`, err.Error())
+
+data, _ := json.Marshal(jsonpJSON.Data) // error was returned while writing data
+ew.bufString = string(data)
+err = jsonpJSON.Render(ew)
+assert.Equal(t, `write "`+string(data)+`" error`, err.Error())
+
+ew.bufString = `);`
+err = jsonpJSON.Render(ew)
+assert.Equal(t, `write "`+`);`+`" error`, err.Error())
+}
+
 func TestRenderJsonpJSONError2(t *testing.T) {
 w := httptest.NewRecorder()
 data := map[string]any{