Add functions to assist in immutability of Event objects

spec/unit/models/event.spec.ts

@@ -0,0 +1,60 @@
+/*
+Copyright 2021 The Matrix.org Foundation C.I.C.
+
+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.
+*/
+
+import { MatrixEvent } from "../../../src/models/event";
+
+describe('MatrixEvent', () => {
+    it('should create copies of itself', () => {
+        const a = new MatrixEvent({
+            type: "com.example.test",
+            content: {
+                isTest: true,
+                num: 42,
+            },
+        });
+
+        const clone = a.getSnapshotCopy();
+        expect(clone).toBeDefined();
+        expect(clone).not.toBe(a);
+        expect(clone.event).not.toBe(a.event);
+        expect(clone.event).toMatchObject(a.event);
+
+        // The other properties we're not super interested in, honestly.
+    });
+
+    it('should compare itself to other events using json', () => {
+        const a = new MatrixEvent({
+            type: "com.example.test",
+            content: {
+                isTest: true,
+                num: 42,
+            },
+        });
+        const b = new MatrixEvent({
+            type: "com.example.test______B",
+            content: {
+                isTest: true,
+                num: 42,
+            },
+        });
+        expect(a.isEquivalentTo(b)).toBe(false);
+        expect(a.isEquivalentTo(a)).toBe(true);
+        expect(b.isEquivalentTo(a)).toBe(false);
+        expect(b.isEquivalentTo(b)).toBe(true);
+        expect(a.getSnapshotCopy().isEquivalentTo(a)).toBe(true);
+        expect(a.getSnapshotCopy().isEquivalentTo(b)).toBe(false);
+    });
+});