feat(external-endpoint): Implement heartbeat (#1173)

Fixes #741

storage/store/memory/memory_test.go

@@ -84,6 +84,7 @@ var (
 // This test is simply an extra sanity check
 func TestStore_SanityCheck(t *testing.T) {
 	store, _ := NewStore(storage.DefaultMaximumNumberOfResults, storage.DefaultMaximumNumberOfEvents)
+	defer store.Clear()
 	defer store.Close()
 	store.Insert(&testEndpoint, &testSuccessfulResult)
 	endpointStatuses, _ := store.GetAllEndpointStatuses(paging.NewEndpointStatusParams())
@@ -134,3 +135,30 @@ func TestStore_Save(t *testing.T) {
 	store.Clear()
 	store.Close()
 }
+
+func TestStore_HasEndpointStatusNewerThan(t *testing.T) {
+	store, _ := NewStore(storage.DefaultMaximumNumberOfResults, storage.DefaultMaximumNumberOfEvents)
+	defer store.Clear()
+	defer store.Close()
+	// Insert a result
+	err := store.Insert(&testEndpoint, &testSuccessfulResult)
+	if err != nil {
+		t.Fatalf("expected no error while inserting result, got %v", err)
+	}
+	// Check with a timestamp in the past
+	hasNewerStatus, err := store.HasEndpointStatusNewerThan(testEndpoint.Key(), time.Now().Add(-time.Hour))
+	if err != nil {
+		t.Fatalf("expected no error, got %v", err)
+	}
+	if !hasNewerStatus {
+		t.Fatal("expected to have a newer status, but didn't")
+	}
+	// Check with a timestamp in the future
+	hasNewerStatus, err = store.HasEndpointStatusNewerThan(testEndpoint.Key(), time.Now().Add(time.Hour))
+	if err != nil {
+		t.Fatalf("expected no error, got %v", err)
+	}
+	if hasNewerStatus {
+		t.Fatal("expected not to have a newer status, but did")
+	}
+}