diff --git a/test/maps-test.ts b/test/maps-test.ts
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+++ b/test/maps-test.ts
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+/*
+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 {EnhancedMap, mapDiff, mapKeyChanges} from "../src/utils/maps";
+
+describe('maps', () => {
+    describe('mapDiff', () => {
+        it('should indicate no differences when the pointers are the same', () => {
+            const a = new Map([[1, 1], [2, 2], [3, 3]]);
+            const result = mapDiff(a, a);
+            expect(result).toBeDefined();
+            expect(result.added).toBeDefined();
+            expect(result.removed).toBeDefined();
+            expect(result.changed).toBeDefined();
+            expect(result.added).toHaveLength(0);
+            expect(result.removed).toHaveLength(0);
+            expect(result.changed).toHaveLength(0);
+        });
+
+        it('should indicate no differences when there are none', () => {
+            const a = new Map([[1, 1], [2, 2], [3, 3]]);
+            const b = new Map([[1, 1], [2, 2], [3, 3]]);
+            const result = mapDiff(a, b);
+            expect(result).toBeDefined();
+            expect(result.added).toBeDefined();
+            expect(result.removed).toBeDefined();
+            expect(result.changed).toBeDefined();
+            expect(result.added).toHaveLength(0);
+            expect(result.removed).toHaveLength(0);
+            expect(result.changed).toHaveLength(0);
+        });
+
+        it('should indicate added properties', () => {
+            const a = new Map([[1, 1], [2, 2], [3, 3]]);
+            const b = new Map([[1, 1], [2, 2], [3, 3], [4, 4]]);
+            const result = mapDiff(a, b);
+            expect(result).toBeDefined();
+            expect(result.added).toBeDefined();
+            expect(result.removed).toBeDefined();
+            expect(result.changed).toBeDefined();
+            expect(result.added).toHaveLength(1);
+            expect(result.removed).toHaveLength(0);
+            expect(result.changed).toHaveLength(0);
+            expect(result.added).toEqual([4]);
+        });
+
+        it('should indicate removed properties', () => {
+            const a = new Map([[1, 1], [2, 2], [3, 3]]);
+            const b = new Map([[1, 1], [2, 2]]);
+            const result = mapDiff(a, b);
+            expect(result).toBeDefined();
+            expect(result.added).toBeDefined();
+            expect(result.removed).toBeDefined();
+            expect(result.changed).toBeDefined();
+            expect(result.added).toHaveLength(0);
+            expect(result.removed).toHaveLength(1);
+            expect(result.changed).toHaveLength(0);
+            expect(result.removed).toEqual([3]);
+        });
+
+        it('should indicate changed properties', () => {
+            const a = new Map([[1, 1], [2, 2], [3, 3]]);
+            const b = new Map([[1, 1], [2, 2], [3, 4]]); // note change
+            const result = mapDiff(a, b);
+            expect(result).toBeDefined();
+            expect(result.added).toBeDefined();
+            expect(result.removed).toBeDefined();
+            expect(result.changed).toBeDefined();
+            expect(result.added).toHaveLength(0);
+            expect(result.removed).toHaveLength(0);
+            expect(result.changed).toHaveLength(1);
+            expect(result.changed).toEqual([3]);
+        });
+
+        it('should indicate changed, added, and removed properties', () => {
+            const a = new Map([[1, 1], [2, 2], [3, 3]]);
+            const b = new Map([[1, 1], [2, 8], [4, 4]]); // note change
+            const result = mapDiff(a, b);
+            expect(result).toBeDefined();
+            expect(result.added).toBeDefined();
+            expect(result.removed).toBeDefined();
+            expect(result.changed).toBeDefined();
+            expect(result.added).toHaveLength(1);
+            expect(result.removed).toHaveLength(1);
+            expect(result.changed).toHaveLength(1);
+            expect(result.added).toEqual([4]);
+            expect(result.removed).toEqual([3]);
+            expect(result.changed).toEqual([2]);
+        });
+
+        it('should indicate changes for difference in pointers', () => {
+            const a = new Map([[1, {}]]); // {} always creates a new object
+            const b = new Map([[1, {}]]);
+            const result = mapDiff(a, b);
+            expect(result).toBeDefined();
+            expect(result.added).toBeDefined();
+            expect(result.removed).toBeDefined();
+            expect(result.changed).toBeDefined();
+            expect(result.added).toHaveLength(0);
+            expect(result.removed).toHaveLength(0);
+            expect(result.changed).toHaveLength(1);
+            expect(result.changed).toEqual([1]);
+        });
+    });
+
+    describe('mapKeyChanges', () => {
+        it('should indicate no changes for unchanged pointers', () => {
+            const a = new Map([[1, 1], [2, 2], [3, 3]]);
+            const result = mapKeyChanges(a, a);
+            expect(result).toBeDefined();
+            expect(result).toHaveLength(0);
+        });
+
+        it('should indicate no changes for unchanged maps with different pointers', () => {
+            const a = new Map([[1, 1], [2, 2], [3, 3]]);
+            const b = new Map([[1, 1], [2, 2], [3, 3]]);
+            const result = mapKeyChanges(a, b);
+            expect(result).toBeDefined();
+            expect(result).toHaveLength(0);
+        });
+
+        it('should indicate changes for added properties', () => {
+            const a = new Map([[1, 1], [2, 2], [3, 3]]);
+            const b = new Map([[1, 1], [2, 2], [3, 3], [4, 4]]);
+            const result = mapKeyChanges(a, b);
+            expect(result).toBeDefined();
+            expect(result).toHaveLength(1);
+            expect(result).toEqual([4]);
+        });
+
+        it('should indicate changes for removed properties', () => {
+            const a = new Map([[1, 1], [2, 2], [3, 3], [4, 4]]);
+            const b = new Map([[1, 1], [2, 2], [3, 3]]);
+            const result = mapKeyChanges(a, b);
+            expect(result).toBeDefined();
+            expect(result).toHaveLength(1);
+            expect(result).toEqual([4]);
+        });
+
+        it('should indicate changes for changed properties', () => {
+            const a = new Map([[1, 1], [2, 2], [3, 3], [4, 4]]);
+            const b = new Map([[1, 1], [2, 2], [3, 3], [4, 55]]);
+            const result = mapKeyChanges(a, b);
+            expect(result).toBeDefined();
+            expect(result).toHaveLength(1);
+            expect(result).toEqual([4]);
+        });
+
+        it('should indicate changes for properties with different pointers', () => {
+            const a = new Map([[1, {}]]); // {} always creates a new object
+            const b = new Map([[1, {}]]);
+            const result = mapKeyChanges(a, b);
+            expect(result).toBeDefined();
+            expect(result).toHaveLength(1);
+            expect(result).toEqual([1]);
+        });
+
+        it('should indicate changes for changed, added, and removed properties', () => {
+            const a = new Map([[1, 1], [2, 2], [3, 3]]);
+            const b = new Map([[1, 1], [2, 8], [4, 4]]); // note change
+            const result = mapKeyChanges(a, b);
+            expect(result).toBeDefined();
+            expect(result).toHaveLength(3);
+            expect(result).toEqual([3, 4, 2]); // order irrelevant, but the test cares
+        });
+    });
+
+    describe('EnhancedMap', () => {
+        // Most of these tests will make sure it implements the Map<K, V> class
+
+        it('should be empty by default', () => {
+            const result = new EnhancedMap();
+            expect(result.size).toBe(0);
+        });
+
+        it('should use the provided entries', () => {
+            const obj = {a: 1, b: 2};
+            const result = new EnhancedMap(Object.entries(obj));
+            expect(result.size).toBe(2);
+            expect(result.get('a')).toBe(1);
+            expect(result.get('b')).toBe(2);
+        });
+
+        it('should create keys if they do not exist', () => {
+            const key = 'a';
+            const val = {}; // we'll check pointers
+
+            const result = new EnhancedMap<string, any>();
+            expect(result.size).toBe(0);
+
+            let get = result.getOrCreate(key, val);
+            expect(get).toBeDefined();
+            expect(get).toBe(val);
+            expect(result.size).toBe(1);
+
+            get = result.getOrCreate(key, 44); // specifically change `val`
+            expect(get).toBeDefined();
+            expect(get).toBe(val);
+            expect(result.size).toBe(1);
+
+            get = result.get(key); // use the base class function
+            expect(get).toBeDefined();
+            expect(get).toBe(val);
+            expect(result.size).toBe(1);
+        });
+
+        it('should proxy remove to delete and return it', () => {
+            const val = {};
+            const result = new EnhancedMap<string, any>();
+            result.set('a', val);
+
+            expect(result.size).toBe(1);
+
+            const removed = result.remove('a');
+            expect(result.size).toBe(0);
+            expect(removed).toBeDefined();
+            expect(removed).toBe(val);
+        });
+
+        it('should support removing unknown keys', () => {
+            const val = {};
+            const result = new EnhancedMap<string, any>();
+            result.set('a', val);
+
+            expect(result.size).toBe(1);
+
+            const removed = result.remove('not-a');
+            expect(result.size).toBe(1);
+            expect(removed).not.toBeDefined();
+        });
+    });
+});