diff --git a/runtime/testing/initializeMockApp.test.js b/runtime/testing/initializeMockApp.test.ts
similarity index 100%
rename from runtime/testing/initializeMockApp.test.js
rename to runtime/testing/initializeMockApp.test.ts
index 5e5b1866..ca947b57 100644
--- a/runtime/testing/initializeMockApp.test.js
+++ b/runtime/testing/initializeMockApp.test.ts
@@ -1,14 +1,13 @@
-import initializeMockApp from './initializeMockApp';
 import {
   getAnalyticsService,
   MockAnalyticsService,
   sendTrackEvent,
 } from '../analytics';
 import {
-  MockAuthService,
   ensureAuthenticatedUser,
   getAuthService,
   getLoginRedirectUrl,
+  MockAuthService,
   setAuthenticatedUser,
 } from '../auth';
 import {
@@ -16,6 +15,7 @@ import {
   logInfo,
   MockLoggingService,
 } from '../logging';
+import initializeMockApp from './initializeMockApp';
 
 describe('initializeMockApp', () => {
   it('should create mock analytics, auth, and logging services, and a real i18n service', () => {
diff --git a/runtime/testing/initializeMockApp.js b/runtime/testing/initializeMockApp.ts
similarity index 96%
rename from runtime/testing/initializeMockApp.js
rename to runtime/testing/initializeMockApp.ts
index c4eeb13c..27e244b6 100644
--- a/runtime/testing/initializeMockApp.js
+++ b/runtime/testing/initializeMockApp.ts
@@ -1,3 +1,4 @@
+// @ts-expect-error We're using an alias in the jest config to create this 'fake' package; TS doesn't know about it.
 import siteConfig from 'site.config';
 
 import { configure as configureAnalytics, MockAnalyticsService } from '../analytics';
diff --git a/runtime/testing/mockMessages.js b/runtime/testing/mockMessages.ts
similarity index 100%
rename from runtime/testing/mockMessages.js
rename to runtime/testing/mockMessages.ts