diff --git a/packages/taler-wallet-core/src/crypto/workers/cryptoDispatcher.ts b/packages/taler-wallet-core/src/crypto/workers/cryptoDispatcher.ts
index f5782ab09..f6c8ae61e 100644
--- a/packages/taler-wallet-core/src/crypto/workers/cryptoDispatcher.ts
+++ b/packages/taler-wallet-core/src/crypto/workers/cryptoDispatcher.ts
@@ -23,7 +23,7 @@
  * Imports.
  */
 import { Logger } from "@gnu-taler/taler-util";
-import * as timer from "../../util/timer.js";
+import { timer, performanceNow, TimerHandle } from "../../util/timer.js";
 import { nullCrypto, TalerCryptoInterface } from "../cryptoImplementation.js";
 import { CryptoWorker } from "./cryptoWorkerInterface.js";
 
@@ -46,7 +46,7 @@ interface WorkerState {
   /**
    * Timer to terminate the worker if it's not busy enough.
    */
-  idleTimeoutHandle: timer.TimerHandle | null;
+  idleTimeoutHandle: TimerHandle | null;
 }
 
 interface WorkItem {
@@ -166,7 +166,7 @@ export class CryptoDispatcher {
       operation: work.operation,
     };
     this.resetWorkerTimeout(ws);
-    work.startTime = timer.performanceNow();
+    work.startTime = performanceNow();
     timer.after(0, () => worker.postMessage(msg));
   }
 
diff --git a/packages/taler-wallet-core/src/headless/helpers.ts b/packages/taler-wallet-core/src/headless/helpers.ts
index 7bc8235fd..180d19859 100644
--- a/packages/taler-wallet-core/src/headless/helpers.ts
+++ b/packages/taler-wallet-core/src/headless/helpers.ts
@@ -36,6 +36,7 @@ import { NodeThreadCryptoWorkerFactory } from "../crypto/workers/nodeThreadWorke
 import { SynchronousCryptoWorkerFactory } from "../crypto/workers/synchronousWorkerFactory.js";
 import { openTalerDatabase } from "../db-utils.js";
 import { HttpRequestLibrary } from "../util/http.js";
+import { SetTimeoutTimerAPI } from "../util/timer.js";
 import { Wallet } from "../wallet.js";
 import { NodeHttpLib } from "./NodeHttpLib.js";
 
@@ -176,7 +177,10 @@ export async function getDefaultNodeWallet2(
       workerFactory = new SynchronousCryptoWorkerFactory();
     }
   }
-  const w = await Wallet.create(myDb, myHttpLib, workerFactory);
+
+  const timer = new SetTimeoutTimerAPI()
+
+  const w = await Wallet.create(myDb, myHttpLib, timer, workerFactory);
 
   if (args.notifyHandler) {
     w.addNotificationListener(args.notifyHandler);
diff --git a/packages/taler-wallet-core/src/util/timer.ts b/packages/taler-wallet-core/src/util/timer.ts
index d9fe3439b..c850c663c 100644
--- a/packages/taler-wallet-core/src/util/timer.ts
+++ b/packages/taler-wallet-core/src/util/timer.ts
@@ -42,7 +42,7 @@ export interface TimerHandle {
 }
 
 class IntervalHandle {
-  constructor(public h: any) {}
+  constructor(public h: any) { }
 
   clear(): void {
     clearInterval(this.h);
@@ -60,7 +60,7 @@ class IntervalHandle {
 }
 
 class TimeoutHandle {
-  constructor(public h: any) {}
+  constructor(public h: any) { }
 
   clear(): void {
     clearTimeout(this.h);
@@ -97,20 +97,6 @@ export const performanceNow: () => bigint = (() => {
   return () => BigInt(0);
 })();
 
-/**
- * Call a function every time the delay given in milliseconds passes.
- */
-export function every(delayMs: number, callback: () => void): TimerHandle {
-  return new IntervalHandle(setInterval(callback, delayMs));
-}
-
-/**
- * Call a function after the delay given in milliseconds passes.
- */
-export function after(delayMs: number, callback: () => void): TimerHandle {
-  return new TimeoutHandle(setTimeout(callback, delayMs));
-}
-
 const nullTimerHandle = {
   clear() {
     // do nothing
@@ -125,13 +111,43 @@ const nullTimerHandle = {
 /**
  * Group of timers that can be destroyed at once.
  */
+export interface TimerAPI {
+  after(delayMs: number, callback: () => void): TimerHandle;
+  every(delayMs: number, callback: () => void): TimerHandle;
+}
+
+export class SetTimeoutTimerAPI implements TimerAPI {
+  /**
+   * Call a function every time the delay given in milliseconds passes.
+   */
+  every(delayMs: number, callback: () => void): TimerHandle {
+    return new IntervalHandle(setInterval(callback, delayMs));
+  }
+
+  /**
+   * Call a function after the delay given in milliseconds passes.
+   */
+  after(delayMs: number, callback: () => void): TimerHandle {
+    return new TimeoutHandle(setTimeout(callback, delayMs));
+  }
+
+
+}
+
+export const timer = new SetTimeoutTimerAPI();
+
+/**
+ * Implementation of [[TimerGroup]] using setTimeout
+ */
 export class TimerGroup {
   private stopped = false;
 
-  private timerMap: { [index: number]: TimerHandle } = {};
+  private readonly timerMap: { [index: number]: TimerHandle } = {};
 
   private idGen = 1;
 
+  constructor(public readonly timerApi: TimerAPI) { }
+
   stopCurrentAndFutureTimers(): void {
     this.stopped = true;
     for (const x in this.timerMap) {
@@ -158,7 +174,7 @@ export class TimerGroup {
       logger.warn("dropping timer since timer group is stopped");
       return nullTimerHandle;
     }
-    const h = after(delayMs, callback);
+    const h = this.timerApi.after(delayMs, callback);
     const myId = this.idGen++;
     this.timerMap[myId] = h;
 
@@ -180,7 +196,7 @@ export class TimerGroup {
       logger.warn("dropping timer since timer group is stopped");
       return nullTimerHandle;
     }
-    const h = every(delayMs, callback);
+    const h = this.timerApi.every(delayMs, callback);
     const myId = this.idGen++;
     this.timerMap[myId] = h;
 
diff --git a/packages/taler-wallet-core/src/wallet.ts b/packages/taler-wallet-core/src/wallet.ts
index 673a86167..e17bbb805 100644
--- a/packages/taler-wallet-core/src/wallet.ts
+++ b/packages/taler-wallet-core/src/wallet.ts
@@ -192,7 +192,7 @@ import {
   openPromise,
 } from "./util/promiseUtils.js";
 import { DbAccess, GetReadWriteAccess } from "./util/query.js";
-import { TimerGroup } from "./util/timer.js";
+import { TimerAPI, TimerGroup } from "./util/timer.js";
 import { WalletCoreApiClient } from "./wallet-api-types.js";
 import { TalerCryptoInterface } from "./crypto/cryptoImplementation.js";
 
@@ -1080,9 +1080,10 @@ export class Wallet {
   private constructor(
     db: DbAccess<typeof WalletStoresV1>,
     http: HttpRequestLibrary,
+    timer: TimerAPI,
     cryptoWorkerFactory: CryptoWorkerFactory,
   ) {
-    this.ws = new InternalWalletStateImpl(db, http, cryptoWorkerFactory);
+    this.ws = new InternalWalletStateImpl(db, http, timer, cryptoWorkerFactory);
   }
 
   get client(): WalletCoreApiClient {
@@ -1100,9 +1101,10 @@ export class Wallet {
   static async create(
     db: DbAccess<typeof WalletStoresV1>,
     http: HttpRequestLibrary,
+    timer: TimerAPI,
     cryptoWorkerFactory: CryptoWorkerFactory,
   ): Promise<Wallet> {
-    const w = new Wallet(db, http, cryptoWorkerFactory);
+    const w = new Wallet(db, http, timer, cryptoWorkerFactory);
     w._client = await getClientFromWalletState(w.ws);
     return w;
   }
@@ -1153,7 +1155,7 @@ class InternalWalletStateImpl implements InternalWalletState {
 
   insecureTrustExchange = false;
 
-  timerGroup: TimerGroup = new TimerGroup();
+  readonly timerGroup: TimerGroup;
   latch = new AsyncCondition();
   stopped = false;
 
@@ -1200,10 +1202,12 @@ class InternalWalletStateImpl implements InternalWalletState {
     // and throw an error in that case.
     public db: DbAccess<typeof WalletStoresV1>,
     public http: HttpRequestLibrary,
+    public timer: TimerAPI,
     cryptoWorkerFactory: CryptoWorkerFactory,
   ) {
     this.cryptoDispatcher = new CryptoDispatcher(cryptoWorkerFactory);
     this.cryptoApi = this.cryptoDispatcher.cryptoApi;
+    this.timerGroup = new TimerGroup(timer)
   }
 
   async getDenomInfo(