test: add reload test

This test reloads the Alertmanager to verify, that it properly keeps
state and sends notifications correctly across reloads.

test/acceptance/send_test.go

@@ -402,3 +402,48 @@ receivers:
 
 	at.Run()
 }
+
+func TestReload(t *testing.T) {
+	t.Parallel()
+
+	// We create a notification config that fans out into two different
+	// webhooks.
+	// The succeeding one must still only receive the first successful
+	// notifications. Sending to the succeeding one must eventually succeed.
+	conf := `
+route:
+  receiver: "default"
+  group_by: []
+  group_wait:      1s
+  group_interval:  6s
+  repeat_interval: 10m
+
+receivers:
+- name: "default"
+  webhook_configs:
+  - url: 'http://%s'
+`
+
+	at := NewAcceptanceTest(t, &AcceptanceOpts{
+		Tolerance: 150 * time.Millisecond,
+	})
+
+	co := at.Collector("webhook")
+	wh := NewWebhook(co)
+
+	am := at.Alertmanager(fmt.Sprintf(conf, wh.Address()))
+
+	am.Push(At(1), Alert("alertname", "test1"))
+	at.Do(At(3), am.Reload)
+	am.Push(At(4), Alert("alertname", "test2"))
+
+	co.Want(Between(2, 2.5), Alert("alertname", "test1").Active(1))
+	// Timers are reset on reload regardless, so we count the 6 second group
+	// interval from 3 onwards.
+	co.Want(Between(9, 9.5),
+		Alert("alertname", "test1").Active(1),
+		Alert("alertname", "test2").Active(4),
+	)
+
+	at.Run()
+}

test/mock.go

@@ -238,6 +238,7 @@ func NewWebhook(c *Collector) *MockWebhook {
 	wh := &MockWebhook{
 		listener:  l,
 		collector: c,
+		opts:      c.opts,
 	}
 	go http.Serve(l, wh)