test: Add fail case for Proxy remote write

Signed-off-by: Philip Gough <[email protected]>

internal/remotewrite/proxy_test.go

@@ -0,0 +1,62 @@
+package remotewrite
+
+import (
+	"bytes"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"testing"
+
+	"github.com/observatorium/observatorium/internal"
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+func TestProxy(t *testing.T) {
+	logger := internal.NewLogger("debug", "logfmt", "test")
+
+	// remoteWriteMain is the primary remote write endpoint that always returns 403 Forbidden.
+	remoteWriteMain := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		logger.Log("msg", "remote write main")
+		w.WriteHeader(http.StatusForbidden)
+	}))
+	defer remoteWriteMain.Close()
+
+	// remoteWriteMirror is a secondary remote write endpoint that always returns 403 Forbidden.
+	remoteWriteMirror := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		logger.Log("msg", "remote write mirror")
+		w.WriteHeader(http.StatusForbidden)
+	}))
+	defer remoteWriteMirror.Close()
+
+	reg := prometheus.NewRegistry()
+
+	writeURL, err := url.Parse(remoteWriteMain.URL)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	endpoints := []Endpoint{
+		{
+			Name: "mirror",
+			URL:  remoteWriteMirror.URL,
+		},
+	}
+	gateway := httptest.NewServer(Proxy(writeURL, endpoints, logger, reg))
+	defer gateway.Close()
+
+	req, err := http.NewRequest(http.MethodPost, gateway.URL, bytes.NewBufferString("some metrics here :)"))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	client := http.DefaultClient
+
+	res, err := client.Do(req)
+	if err != nil {
+		t.Fatal(err)
+	}
+	_ = res.Body.Close()
+	if res.StatusCode != http.StatusForbidden {
+		t.Fatalf("expected status code %d, got %d", http.StatusForbidden, res.StatusCode)
+	}
+}