t.Fatal("headers have not been written yet")
	}

	trw.WriteHeader(123)
	if !headersAlreadyWritten(trw) {
		t.Fatal("headers were written")
	}
}

func TestHeadersAlreadyWrittenWrapped(t *testing.T) {
	rw := httptest.NewRecorder()
	trw := &trackingResponseWriter{ResponseWriter: rw}
	wrap1 := &gzhttp.NoGzipResponseWriter{ResponseWriter: trw}