Relocate wrapped ResponseWriter to middleware

internal/middleware/responsewriter/wrap_writer_test.go

@@ -0,0 +1,33 @@
+package responsewriter
+
+import (
+	"net/http/httptest"
+	"testing"
+)
+
+func TestFlushWriterRemembersWroteHeaderWhenFlushed(t *testing.T) {
+	f := &flushWriter{basicWriter{ResponseWriter: httptest.NewRecorder()}}
+	f.Flush()
+
+	if !f.wroteHeader {
+		t.Fatal("want Flush to have set wroteHeader=true")
+	}
+}
+
+func TestHttpFancyWriterRemembersWroteHeaderWhenFlushed(t *testing.T) {
+	f := &httpFancyWriter{basicWriter{ResponseWriter: httptest.NewRecorder()}}
+	f.Flush()
+
+	if !f.wroteHeader {
+		t.Fatal("want Flush to have set wroteHeader=true")
+	}
+}
+
+func TestHttp2FancyWriterRemembersWroteHeaderWhenFlushed(t *testing.T) {
+	f := &http2FancyWriter{basicWriter{ResponseWriter: httptest.NewRecorder()}}
+	f.Flush()
+
+	if !f.wroteHeader {
+		t.Fatal("want Flush to have set wroteHeader=true")
+	}
+}