Add test case for Flush (http.Flusher)

gzip_test.go

@@ -241,6 +241,49 @@ func TestStatusCodes(t *testing.T) {
 	assert.Equal(t, http.StatusOK, result.StatusCode)
 }
 
+type httpFlusherFunc func()
+
+func (fn httpFlusherFunc) Flush() { fn() }
+
+func TestFlush(t *testing.T) {
+	b := []byte(testBody)
+	handler := Gzip(http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
+		rw.WriteHeader(http.StatusNotFound)
+		rw.Write(b)
+		rw.(http.Flusher).Flush()
+		rw.Write(b)
+	}), MinSize(0), CompressionLevel(DefaultCompression))
+
+	r := httptest.NewRequest(http.MethodGet, "/", nil)
+	r.Header.Set("Accept-Encoding", "gzip")
+	w := httptest.NewRecorder()
+
+	var flushed bool
+	handler.ServeHTTP(struct {
+		http.ResponseWriter
+		http.Flusher
+	}{
+		w,
+		httpFlusherFunc(func() { flushed = true }),
+	}, r)
+
+	assert.True(t, flushed, "Flush did not call underlying http.Flusher")
+
+	res := w.Result()
+	assert.Equal(t, http.StatusNotFound, res.StatusCode)
+	assert.Equal(t, "gzip", res.Header.Get("Content-Encoding"))
+
+	var buf bytes.Buffer
+	gw, _ := gzip.NewWriterLevel(&buf, DefaultCompression)
+
+	gw.Write(b)
+	gw.Flush() // Flush emits a symbol into the deflate output
+	gw.Write(b)
+	gw.Close()
+
+	assert.Equal(t, buf.Bytes(), w.Body.Bytes())
+}
+
 func TestFlushBeforeWrite(t *testing.T) {
 	b := []byte(testBody)
 	handler := Gzip(http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {