added test of Hijack()

response_writer_test.go

@@ -5,6 +5,8 @@
 package gin
 
 import (
+	"bufio"
+	"net"
 	"net/http"
 	"net/http/httptest"
 	"testing"
@@ -124,6 +126,45 @@ func TestResponseWriterHijack(t *testing.T) {
 	w.Flush()
 }
 
+type mockHijacker struct {
+	*httptest.ResponseRecorder
+	hijacked bool
+}
+
+func (m *mockHijacker) Hijack() (net.Conn, *bufio.ReadWriter, error) {
+	m.hijacked = true
+	return nil, nil, nil
+}
+
+func TestResponseWriterHijackAfterWrite(t *testing.T) {
+	// Test case 1: Hijack before writing
+	hijacker := &mockHijacker{ResponseRecorder: httptest.NewRecorder()}
+	writer := &responseWriter{}
+	writer.reset(hijacker)
+	w := ResponseWriter(writer)
+
+	_, _, err := w.Hijack()
+	require.NoError(t, err)
+	assert.True(t, hijacker.hijacked, "Hijack should be called")
+	assert.True(t, w.Written(), "Written() should be true after Hijack")
+
+	// Test case 2: Hijack after writing
+	hijacker2 := &mockHijacker{ResponseRecorder: httptest.NewRecorder()}
+	writer2 := &responseWriter{}
+	writer2.reset(hijacker2)
+	w2 := ResponseWriter(writer2)
+
+	_, err = w2.Write([]byte("test"))
+	require.NoError(t, err)
+	assert.True(t, w2.Written(), "Written() should be true after Write")
+
+	// Now, try to hijack
+	_, _, err = w2.Hijack()
+	require.Error(t, err)
+	assert.Equal(t, errHijackAlreadyWritten, err, "Hijack after write should return errHijackAlreadyWritten")
+	assert.False(t, hijacker2.hijacked, "Hijack should not be called after write")
+}
+
 func TestResponseWriterFlush(t *testing.T) {
 	testServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		writer := &responseWriter{}