test: add table-driven tests for ReceiverServer

Adds httptest-based unit tests for receiver_server.go covering:
- NewReceiverServer constructor field validation
- ListenAndServe routing: unknown hook token → 404, non-hook path → 404,
  exportHTTPPathMetrics variant → 404
- Graceful shutdown via stop channel
- Webhook path routing dispatches to handlePayload (not 404)

Each subtest uses a private Prometheus registry to avoid duplicate
metric registration panics. Addresses #496.

Signed-off-by: Hamza Younas <hamza.younas94@gmail.com>

Author: hamza-younas94

internal/server/receiver_server_test.go

@@ -0,0 +1,220 @@
+/*
+Copyright 2024 The Flux authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package server
+
+import (
+	"net"
+	"net/http"
+	"strconv"
+	"testing"
+	"time"
+
+	. "github.com/onsi/gomega"
+	"github.com/prometheus/client_golang/prometheus"
+	prommetrics "github.com/slok/go-http-metrics/metrics/prometheus"
+	"github.com/slok/go-http-metrics/middleware"
+	corev1 "k8s.io/api/core/v1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/runtime"
+	fakeclient "sigs.k8s.io/controller-runtime/pkg/client/fake"
+	log "sigs.k8s.io/controller-runtime/pkg/log"
+
+	apimeta "github.com/fluxcd/pkg/apis/meta"
+	"github.com/fluxcd/pkg/apis/meta"
+
+	apiv1 "github.com/fluxcd/notification-controller/api/v1"
+)
+
+// newTestReceiverServer creates a ReceiverServer listening on a free port and
+// returns the server, its base URL and a stop channel.  The caller must close
+// the stop channel to shut the server down.
+func newTestReceiverServer(t *testing.T, exportHTTPPathMetrics bool, objs ...runtime.Object) (*ReceiverServer, string, chan struct{}) {
+	t.Helper()
+	g := NewWithT(t)
+
+	scheme := runtime.NewScheme()
+	g.Expect(corev1.AddToScheme(scheme)).To(Succeed())
+	g.Expect(apiv1.AddToScheme(scheme)).To(Succeed())
+
+	builder := fakeclient.NewClientBuilder().WithScheme(scheme).
+		WithIndex(&apiv1.Receiver{}, WebhookPathIndexKey, IndexReceiverWebhookPath)
+	for _, o := range objs {
+		builder = builder.WithRuntimeObjects(o)
+	}
+	kc := builder.Build()
+
+	l, err := net.Listen("tcp", "127.0.0.1:0")
+	g.Expect(err).ToNot(HaveOccurred())
+	port := strconv.Itoa(l.Addr().(*net.TCPAddr).Port)
+	g.Expect(l.Close()).ToNot(HaveOccurred())
+
+	// Use a fresh private Prometheus registry per test to avoid duplicate
+	// metric registration panics when subtests each create a new server.
+	mdlw := middleware.New(middleware.Config{
+		Recorder: prommetrics.NewRecorder(prommetrics.Config{
+			Prefix:   "gotk_receiver_test",
+			Registry: prometheus.NewRegistry(),
+		}),
+	})
+
+	srv := NewReceiverServer(
+		"127.0.0.1:"+port,
+		log.Log,
+		kc,
+		false,
+		exportHTTPPathMetrics,
+	)
+	stopCh := make(chan struct{})
+	go srv.ListenAndServe(stopCh, mdlw)
+
+	// Wait until the server is ready.
+	baseURL := "http://127.0.0.1:" + port
+	g.Eventually(func() error {
+		resp, err := http.Get(baseURL + "/")
+		if err != nil {
+			return err
+		}
+		resp.Body.Close()
+		return nil
+	}, 5*time.Second, 100*time.Millisecond).Should(Succeed())
+
+	return srv, baseURL, stopCh
+}
+
+func TestNewReceiverServer(t *testing.T) {
+	g := NewWithT(t)
+
+	scheme := runtime.NewScheme()
+	g.Expect(corev1.AddToScheme(scheme)).To(Succeed())
+	g.Expect(apiv1.AddToScheme(scheme)).To(Succeed())
+
+	kc := fakeclient.NewClientBuilder().WithScheme(scheme).Build()
+
+	srv := NewReceiverServer(":9292", log.Log, kc, true, true)
+	g.Expect(srv).ToNot(BeNil())
+	g.Expect(srv.port).To(Equal(":9292"))
+	g.Expect(srv.kubeClient).ToNot(BeNil())
+	g.Expect(srv.noCrossNamespaceRefs).To(BeTrue())
+	g.Expect(srv.exportHTTPPathMetrics).To(BeTrue())
+}
+
+func TestReceiverServer_ListenAndServe(t *testing.T) {
+	tests := []struct {
+		name                  string
+		path                  string
+		exportHTTPPathMetrics bool
+		wantStatus            int
+	}{
+		{
+			name:       "unknown hook path returns 404",
+			path:       apiv1.ReceiverWebhookPath + "unknowntoken",
+			wantStatus: http.StatusNotFound,
+		},
+		{
+			name:       "non-hook path returns 404",
+			path:       "/healthz",
+			wantStatus: http.StatusNotFound,
+		},
+		{
+			name:                  "unknown hook path with exportHTTPPathMetrics returns 404",
+			path:                  apiv1.ReceiverWebhookPath + "unknowntoken",
+			exportHTTPPathMetrics: true,
+			wantStatus:            http.StatusNotFound,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			g := NewWithT(t)
+
+			_, baseURL, stopCh := newTestReceiverServer(t, tt.exportHTTPPathMetrics)
+			defer close(stopCh)
+
+			resp, err := http.Post(baseURL+tt.path, "application/json", nil)
+			g.Expect(err).ToNot(HaveOccurred())
+			resp.Body.Close()
+			g.Expect(resp.StatusCode).To(Equal(tt.wantStatus))
+		})
+	}
+}
+
+func TestReceiverServer_Shutdown(t *testing.T) {
+	g := NewWithT(t)
+
+	_, baseURL, stopCh := newTestReceiverServer(t, false)
+
+	// Server is up.
+	resp, err := http.Get(baseURL + "/")
+	g.Expect(err).ToNot(HaveOccurred())
+	resp.Body.Close()
+
+	// Signal shutdown.
+	close(stopCh)
+
+	// Server should stop accepting connections.
+	g.Eventually(func() error {
+		_, err := http.Get(baseURL + "/")
+		return err
+	}, 5*time.Second, 100*time.Millisecond).ShouldNot(Succeed())
+}
+
+func TestReceiverServer_WebhookPathRouting(t *testing.T) {
+	g := NewWithT(t)
+
+	// Create a Receiver with a known token so handlePayload can look it up.
+	token := "test-token-abc123"
+	secret := &corev1.Secret{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:      "receiver-token",
+			Namespace: "default",
+		},
+		Data: map[string][]byte{
+			"token": []byte(token),
+		},
+	}
+	receiver := &apiv1.Receiver{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:      "test-receiver",
+			Namespace: "default",
+		},
+		Spec: apiv1.ReceiverSpec{
+			Type: apiv1.GenericReceiver,
+			SecretRef: meta.LocalObjectReference{
+				Name: "receiver-token",
+			},
+		},
+		Status: apiv1.ReceiverStatus{
+			WebhookPath: apiv1.ReceiverWebhookPath + token,
+			Conditions: []metav1.Condition{
+				{
+					Type:   apimeta.ReadyCondition,
+					Status: metav1.ConditionTrue,
+				},
+			},
+		},
+	}
+
+	_, baseURL, stopCh := newTestReceiverServer(t, false, secret, receiver)
+	defer close(stopCh)
+
+	// A POST to the webhook path with a valid token should reach handlePayload
+	// and return 200 (GenericReceiver with Ready=True).
+	resp, err := http.Post(baseURL+apiv1.ReceiverWebhookPath+token, "application/json", nil)
+	g.Expect(err).ToNot(HaveOccurred())
+	resp.Body.Close()
+	g.Expect(resp.StatusCode).To(Equal(http.StatusOK))
+}