diff --git a/cmd/prometheus/main.go b/cmd/prometheus/main.go
index 0a255547a8..30cf95088f 100644
--- a/cmd/prometheus/main.go
+++ b/cmd/prometheus/main.go
@@ -696,8 +696,12 @@ func computeExternalURL(u, listenAddr string) (*url.URL, error) {
 	return eu, nil
 }
 
+type sender interface {
+	Send(alerts ...*notifier.Alert)
+}
+
 // sendAlerts implements the rules.NotifyFunc for a Notifier.
-func sendAlerts(n *notifier.Manager, externalURL string) rules.NotifyFunc {
+func sendAlerts(s sender, externalURL string) rules.NotifyFunc {
 	return func(ctx context.Context, expr string, alerts ...*rules.Alert) {
 		var res []*notifier.Alert
 
@@ -717,7 +721,7 @@ func sendAlerts(n *notifier.Manager, externalURL string) rules.NotifyFunc {
 		}
 
 		if len(alerts) > 0 {
-			n.Send(res...)
+			s.Send(res...)
 		}
 	}
 }
diff --git a/cmd/prometheus/main_test.go b/cmd/prometheus/main_test.go
index 605ba816eb..c6697a101f 100644
--- a/cmd/prometheus/main_test.go
+++ b/cmd/prometheus/main_test.go
@@ -14,6 +14,7 @@
 package main
 
 import (
+	"context"
 	"flag"
 	"fmt"
 	"net/http"
@@ -24,6 +25,9 @@ import (
 	"testing"
 	"time"
 
+	"github.com/prometheus/prometheus/notifier"
+	"github.com/prometheus/prometheus/pkg/labels"
+	"github.com/prometheus/prometheus/rules"
 	"github.com/prometheus/prometheus/util/testutil"
 )
 
@@ -173,3 +177,73 @@ func TestFailedStartupExitCode(t *testing.T) {
 		t.Errorf("unable to retrieve the exit status for prometheus: %v", err)
 	}
 }
+
+type senderFunc func(alerts ...*notifier.Alert)
+
+func (s senderFunc) Send(alerts ...*notifier.Alert) {
+	s(alerts...)
+}
+
+func TestSendAlerts(t *testing.T) {
+	testCases := []struct {
+		in  []*rules.Alert
+		exp []*notifier.Alert
+	}{
+		{
+			in: []*rules.Alert{
+				&rules.Alert{
+					Labels:      []labels.Label{{Name: "l1", Value: "v1"}},
+					Annotations: []labels.Label{{Name: "a2", Value: "v2"}},
+					ActiveAt:    time.Unix(1, 0),
+					FiredAt:     time.Unix(2, 0),
+					ValidUntil:  time.Unix(3, 0),
+				},
+			},
+			exp: []*notifier.Alert{
+				&notifier.Alert{
+					Labels:       []labels.Label{{Name: "l1", Value: "v1"}},
+					Annotations:  []labels.Label{{Name: "a2", Value: "v2"}},
+					StartsAt:     time.Unix(2, 0),
+					EndsAt:       time.Unix(3, 0),
+					GeneratorURL: "http://localhost:9090/graph?g0.expr=up&g0.tab=1",
+				},
+			},
+		},
+		{
+			in: []*rules.Alert{
+				&rules.Alert{
+					Labels:      []labels.Label{{Name: "l1", Value: "v1"}},
+					Annotations: []labels.Label{{Name: "a2", Value: "v2"}},
+					ActiveAt:    time.Unix(1, 0),
+					FiredAt:     time.Unix(2, 0),
+					ResolvedAt:  time.Unix(4, 0),
+				},
+			},
+			exp: []*notifier.Alert{
+				&notifier.Alert{
+					Labels:       []labels.Label{{Name: "l1", Value: "v1"}},
+					Annotations:  []labels.Label{{Name: "a2", Value: "v2"}},
+					StartsAt:     time.Unix(2, 0),
+					EndsAt:       time.Unix(4, 0),
+					GeneratorURL: "http://localhost:9090/graph?g0.expr=up&g0.tab=1",
+				},
+			},
+		},
+		{
+			in: []*rules.Alert{},
+		},
+	}
+
+	for i, tc := range testCases {
+		tc := tc
+		t.Run(fmt.Sprintf("%d", i), func(t *testing.T) {
+			senderFunc := senderFunc(func(alerts ...*notifier.Alert) {
+				if len(tc.in) == 0 {
+					t.Fatalf("sender called with 0 alert")
+				}
+				testutil.Equals(t, tc.exp, alerts)
+			})
+			sendAlerts(senderFunc, "http://localhost:9090")(context.TODO(), "up", tc.in...)
+		})
+	}
+}