diff --git a/pkg/model/notificationevent_test.go b/pkg/model/notificationevent_test.go
new file mode 100644
index 0000000000..53e5c43770
--- /dev/null
+++ b/pkg/model/notificationevent_test.go
@@ -0,0 +1,66 @@
+// Copyright 2023 The PipeCD 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 model
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestGroup(t *testing.T) {
+	t.Parallel()
+	tests := []struct {
+		name string
+		typ  NotificationEventType
+		want NotificationEventGroup
+	}{
+		{
+			name: "returns EVENT_DEPLOYMENT for type < 100",
+			typ:  99,
+			want: NotificationEventGroup_EVENT_DEPLOYMENT,
+		},
+		{
+			name: "returns EVENT_APPLICATION_SYNC for type < 200",
+			typ:  199,
+			want: NotificationEventGroup_EVENT_APPLICATION_SYNC,
+		},
+		{
+			name: "returns EVENT_APPLICATION_HEALTH for type < 300",
+			typ:  299,
+			want: NotificationEventGroup_EVENT_APPLICATION_HEALTH,
+		},
+		{
+			name: "returns EVENT_PIPED for type < 400",
+			typ:  399,
+			want: NotificationEventGroup_EVENT_PIPED,
+		},
+		{
+			name: "returns EVENT_NONE for type >= 400",
+			typ:  400,
+			want: NotificationEventGroup_EVENT_NONE,
+		},
+	}
+
+	for _, tt := range tests {
+		tt := tt
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+			e := NotificationEvent{Type: tt.typ}
+			got := e.Group()
+			assert.Equal(t, tt.want, got)
+		})
+	}
+}