diff --git a/test/utils/MegolmExportEncryption-test.js b/test/utils/MegolmExportEncryption-test.ts
similarity index 95%
rename from test/utils/MegolmExportEncryption-test.js
rename to test/utils/MegolmExportEncryption-test.ts
index 8b16085efc..4fb92a8f8b 100644
--- a/test/utils/MegolmExportEncryption-test.js
+++ b/test/utils/MegolmExportEncryption-test.ts
@@ -20,7 +20,8 @@ import { Crypto } from "@peculiar/webcrypto";
 
 const webCrypto = new Crypto();
 
-function getRandomValues(buf) {
+function getRandomValues<T extends ArrayBufferView>(buf: T): T {
+    // @ts-ignore fussy generics
     return nodeCrypto.randomFillSync(buf);
 }
 
@@ -64,7 +65,7 @@ const TEST_VECTORS=[
     ],
 ];
 
-function stringToArray(s) {
+function stringToArray(s: string): ArrayBufferLike {
     return new TextEncoder().encode(s).buffer;
 }
 
@@ -72,7 +73,10 @@ describe('MegolmExportEncryption', function() {
     let MegolmExportEncryption;
 
     beforeAll(() => {
-        window.crypto = { subtle: webCrypto.subtle, getRandomValues };
+        window.crypto = {
+            subtle: webCrypto.subtle,
+            getRandomValues,
+        };
         MegolmExportEncryption = require("../../src/utils/MegolmExportEncryption");
     });
 
diff --git a/test/utils/ShieldUtils-test.js b/test/utils/ShieldUtils-test.ts
similarity index 83%
rename from test/utils/ShieldUtils-test.js
rename to test/utils/ShieldUtils-test.ts
index 85f9de3150..10ccb80f96 100644
--- a/test/utils/ShieldUtils-test.js
+++ b/test/utils/ShieldUtils-test.ts
@@ -1,7 +1,28 @@
+/*
+Copyright 2022 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 {
+    MatrixClient,
+    Room,
+} from 'matrix-js-sdk/src/matrix';
+
 import { shieldStatusForRoom } from '../../src/utils/ShieldUtils';
 import DMRoomMap from '../../src/utils/DMRoomMap';
 
-function mkClient(selfTrust) {
+function mkClient(selfTrust = false) {
     return {
         getUserId: () => "@self:localhost",
         checkUserTrust: (userId) => ({
@@ -12,7 +33,7 @@ function mkClient(selfTrust) {
             isVerified: () => userId === "@self:localhost" ? selfTrust : userId[2] == "T",
         }),
         getStoredDevicesForUser: (userId) => ["DEVICE"],
-    };
+    } as unknown as MatrixClient;
 }
 
 describe("mkClient self-test", function() {
@@ -42,9 +63,14 @@ describe("mkClient self-test", function() {
 
 describe("shieldStatusForMembership self-trust behaviour", function() {
     beforeAll(() => {
-        DMRoomMap.sharedInstance = {
+        const mockInstance = {
             getUserIdForRoomId: (roomId) => roomId === "DM" ? "@any:h" : null,
-        };
+        } as unknown as DMRoomMap;
+        jest.spyOn(DMRoomMap, 'shared').mockReturnValue(mockInstance);
+    });
+
+    afterAll(() => {
+        jest.spyOn(DMRoomMap, 'shared').mockRestore();
     });
 
     it.each(
@@ -55,7 +81,7 @@ describe("shieldStatusForMembership self-trust behaviour", function() {
         const room = {
             roomId: dm ? "DM" : "other",
             getEncryptionTargetMembers: () => ["@self:localhost", "@FF1:h", "@FF2:h"].map((userId) => ({ userId })),
-        };
+        } as unknown as Room;
         const status = await shieldStatusForRoom(client, room);
         expect(status).toEqual("normal");
     });
@@ -68,7 +94,7 @@ describe("shieldStatusForMembership self-trust behaviour", function() {
         const room = {
             roomId: dm ? "DM" : "other",
             getEncryptionTargetMembers: () => ["@self:localhost", "@TT1:h", "@TT2:h"].map((userId) => ({ userId })),
-        };
+        } as unknown as Room;
         const status = await shieldStatusForRoom(client, room);
         expect(status).toEqual(result);
     });
@@ -81,7 +107,7 @@ describe("shieldStatusForMembership self-trust behaviour", function() {
         const room = {
             roomId: dm ? "DM" : "other",
             getEncryptionTargetMembers: () => ["@self:localhost", "@TT1:h", "@FF2:h"].map((userId) => ({ userId })),
-        };
+        } as unknown as Room;
         const status = await shieldStatusForRoom(client, room);
         expect(status).toEqual(result);
     });
@@ -94,7 +120,7 @@ describe("shieldStatusForMembership self-trust behaviour", function() {
         const room = {
             roomId: dm ? "DM" : "other",
             getEncryptionTargetMembers: () => ["@self:localhost"].map((userId) => ({ userId })),
-        };
+        } as unknown as Room;
         const status = await shieldStatusForRoom(client, room);
         expect(status).toEqual(result);
     });
@@ -107,7 +133,7 @@ describe("shieldStatusForMembership self-trust behaviour", function() {
         const room = {
             roomId: dm ? "DM" : "other",
             getEncryptionTargetMembers: () => ["@self:localhost", "@TT:h"].map((userId) => ({ userId })),
-        };
+        } as unknown as Room;
         const status = await shieldStatusForRoom(client, room);
         expect(status).toEqual(result);
     });
@@ -120,7 +146,7 @@ describe("shieldStatusForMembership self-trust behaviour", function() {
         const room = {
             roomId: dm ? "DM" : "other",
             getEncryptionTargetMembers: () => ["@self:localhost", "@FF:h"].map((userId) => ({ userId })),
-        };
+        } as unknown as Room;
         const status = await shieldStatusForRoom(client, room);
         expect(status).toEqual(result);
     });
@@ -128,9 +154,10 @@ describe("shieldStatusForMembership self-trust behaviour", function() {
 
 describe("shieldStatusForMembership other-trust behaviour", function() {
     beforeAll(() => {
-        DMRoomMap.sharedInstance = {
+        const mockInstance = {
             getUserIdForRoomId: (roomId) => roomId === "DM" ? "@any:h" : null,
-        };
+        } as unknown as DMRoomMap;
+        jest.spyOn(DMRoomMap, 'shared').mockReturnValue(mockInstance);
     });
 
     it.each(
@@ -140,7 +167,7 @@ describe("shieldStatusForMembership other-trust behaviour", function() {
         const room = {
             roomId: dm ? "DM" : "other",
             getEncryptionTargetMembers: () => ["@self:localhost", "@TF:h"].map((userId) => ({ userId })),
-        };
+        } as unknown as Room;
         const status = await shieldStatusForRoom(client, room);
         expect(status).toEqual(result);
     });
@@ -152,7 +179,7 @@ describe("shieldStatusForMembership other-trust behaviour", function() {
         const room = {
             roomId: dm ? "DM" : "other",
             getEncryptionTargetMembers: () => ["@self:localhost", "@TF:h", "@TT:h"].map((userId) => ({ userId })),
-        };
+        } as unknown as Room;
         const status = await shieldStatusForRoom(client, room);
         expect(status).toEqual(result);
     });
@@ -164,7 +191,7 @@ describe("shieldStatusForMembership other-trust behaviour", function() {
         const room = {
             roomId: dm ? "DM" : "other",
             getEncryptionTargetMembers: () => ["@self:localhost", "@FF:h", "@FT:h"].map((userId) => ({ userId })),
-        };
+        } as unknown as Room;
         const status = await shieldStatusForRoom(client, room);
         expect(status).toEqual(result);
     });
@@ -176,7 +203,7 @@ describe("shieldStatusForMembership other-trust behaviour", function() {
         const room = {
             roomId: dm ? "DM" : "other",
             getEncryptionTargetMembers: () => ["@self:localhost", "@WF:h", "@FT:h"].map((userId) => ({ userId })),
-        };
+        } as unknown as Room;
         const status = await shieldStatusForRoom(client, room);
         expect(status).toEqual(result);
     });