diff --git a/lib/shared/device-list-utils.test.js b/lib/shared/device-list-utils.test.js
--- a/lib/shared/device-list-utils.test.js
+++ b/lib/shared/device-list-utils.test.js
@@ -3,6 +3,8 @@
 import {
   createAndSignInitialDeviceList,
   verifyAndGetDeviceList,
+  addDeviceToDeviceList,
+  removeDeviceFromDeviceList,
 } from './device-list-utils.js';
 import type {
   RawDeviceList,
@@ -165,6 +167,62 @@
   });
 });
 
+describe(addDeviceToDeviceList, () => {
+  it('adds device to device list', async () => {
+    mockOlmAPISign();
+
+    const updates: $ReadOnlyArray<SignedDeviceList> = [
+      createDeviceList({ devices: ['D1'], timestamp: 1 }),
+    ];
+    const identityClient = mockIdentityClientWithDeviceListHistory(updates);
+
+    await addDeviceToDeviceList(identityClient, 'user1', 'D2');
+
+    expect(identityClient.updateDeviceList).toHaveBeenCalledWith(
+      matchingSignedDeviceListWithDevices(['D1', 'D2']),
+    );
+  });
+
+  it('skips adding device to device list if already exists', async () => {
+    const updates: $ReadOnlyArray<SignedDeviceList> = [
+      createDeviceList({ devices: ['D1', 'D2'], timestamp: 1 }),
+    ];
+    const identityClient = mockIdentityClientWithDeviceListHistory(updates);
+
+    await addDeviceToDeviceList(identityClient, 'user1', 'D2');
+
+    expect(identityClient.updateDeviceList).not.toHaveBeenCalled();
+  });
+});
+
+describe(removeDeviceFromDeviceList, () => {
+  it('removes device from device list', async () => {
+    mockOlmAPISign();
+
+    const updates: $ReadOnlyArray<SignedDeviceList> = [
+      createDeviceList({ devices: ['D1', 'D2'], timestamp: 1 }),
+    ];
+    const identityClient = mockIdentityClientWithDeviceListHistory(updates);
+
+    await removeDeviceFromDeviceList(identityClient, 'user1', 'D2');
+
+    expect(identityClient.updateDeviceList).toHaveBeenCalledWith(
+      matchingSignedDeviceListWithDevices(['D1']),
+    );
+  });
+
+  it("skips removing device from device list if it doesn't exist", async () => {
+    const updates: $ReadOnlyArray<SignedDeviceList> = [
+      createDeviceList({ devices: ['D1'], timestamp: 1 }),
+    ];
+    const identityClient = mockIdentityClientWithDeviceListHistory(updates);
+
+    await removeDeviceFromDeviceList(identityClient, 'user1', 'D2');
+
+    expect(identityClient.updateDeviceList).not.toHaveBeenCalled();
+  });
+});
+
 function createDeviceList(
   rawList: RawDeviceList,
   curPrimarySignature?: string,
@@ -184,6 +242,7 @@
     getDeviceListHistoryForUser: jest
       .fn<any, typeof history>()
       .mockResolvedValueOnce(history),
+    updateDeviceList: jest.fn(),
   };
   return client;
 }
@@ -196,10 +255,32 @@
   config.registerConfig(cfg);
 }
 
-function mockOlmAPISign(func: JestMockFn<[string], Promise<string>>) {
+const defaultOlmAPISignMock = jest
+  .fn<[string], string>()
+  .mockResolvedValue('mock_signature');
+
+function mockOlmAPISign(
+  func: JestMockFn<[string], Promise<string>> = defaultOlmAPISignMock,
+  ed25519: string = 'fake_ed25519_public_key',
+) {
   const olmAPI: any = {
+    initializeCryptoAccount: jest.fn(),
+    getUserPublicKey: jest
+      .fn<[], mixed>()
+      .mockResolvedValue({ primaryIdentityPublicKeys: { ed25519 } }),
     signMessage: func,
   };
   const cfg: any = { olmAPI };
   config.registerConfig(cfg);
 }
+
+function matchingSignedDeviceListWithDevices(
+  devices: $ReadOnlyArray<string>,
+): Object {
+  return expect.objectContaining({
+    rawDeviceList: expect.stringContaining(
+      // slice out closing braces to let it match timestamp
+      JSON.stringify({ devices }).slice(0, -2),
+    ),
+  });
+}