diff --git a/packages/concurrentAsync/index.test.ts b/packages/concurrentAsync/index.test.ts
index 429b6bf..2323c52 100644
--- a/packages/concurrentAsync/index.test.ts
+++ b/packages/concurrentAsync/index.test.ts
@@ -29,40 +29,40 @@ describe('concurrentAsync', () => {
   });
   test('invoked when', async () => {
     jest.useFakeTimers();
-    jest.spyOn(global, 'setTimeout');
+    const rawFn = jest.fn(someAsyncTask);
     // 0,200,400
     // 100,300
-    const con2 = concurrentAsync(someAsyncTask, 2);
+    const con2 = concurrentAsync(rawFn, 2);
     const promises = new Array(5).fill(0).map((_, i) => con2(i * 2, i * 100, i % 2 === 0));
 
-    expect(setTimeout).toHaveBeenCalledTimes(2);
+    expect(rawFn).toHaveBeenCalledTimes(2);
 
     jest.advanceTimersByTime(1);
     await expect(promises[0]).rejects.toBe(0);
     // next task will be created util previous promise is resolved or rejected
-    expect(setTimeout).toHaveBeenCalledTimes(3); // the 3rd task has be created and the 4th hasn't been created yet
+    expect(rawFn).toHaveBeenCalledTimes(3); // the 3rd task has be created and the 4th hasn't been created yet
 
     jest.advanceTimersByTime(50); // 51ms
-    expect(setTimeout).toHaveBeenCalledTimes(3); // no new task(4th) was created
+    expect(rawFn).toHaveBeenCalledTimes(3); // no new task(4th) was created
 
     jest.advanceTimersByTime(50); // 101ms
-    expect(setTimeout).toHaveBeenCalledTimes(3); // no new task(4th) was created
+    expect(rawFn).toHaveBeenCalledTimes(3); // no new task(4th) was created
     await expect(promises[1]).resolves.toBe(2); // the 2nd task was resolved
-    expect(setTimeout).toHaveBeenCalledTimes(4); // the 4th task was created
+    expect(rawFn).toHaveBeenCalledTimes(4); // the 4th task was created
     jest.advanceTimersByTime(50); // 151ms
-    expect(setTimeout).toHaveBeenCalledTimes(4); // no new task(5th) was created
+    expect(rawFn).toHaveBeenCalledTimes(4); // no new task(5th) was created
 
     jest.advanceTimersByTime(50); // 201ms
-    expect(setTimeout).toHaveBeenCalledTimes(4); // no new task(5th) was created
+    expect(rawFn).toHaveBeenCalledTimes(4); // no new task(5th) was created
     await expect(promises[2]).rejects.toBe(4); // the 3rd task was resolved
-    expect(setTimeout).toHaveBeenCalledTimes(5); // the 5th task was created
+    expect(rawFn).toHaveBeenCalledTimes(5); // the 5th task was created
 
     jest.advanceTimersByTime(200); // 401ms
     await expect(promises[3]).resolves.toBe(6); // the 4th task was resolved
-    expect(setTimeout).toHaveBeenCalledTimes(5); // no more task was created
+    expect(rawFn).toHaveBeenCalledTimes(5); // no more task was created
 
     jest.advanceTimersByTime(200); // 601ms
     await expect(promises[4]).rejects.toBe(8); // the 5th task was resolved
-    expect(setTimeout).toHaveBeenCalledTimes(5); // no more task was created
+    expect(rawFn).toHaveBeenCalledTimes(5); // no more task was created
   });
 });
diff --git a/packages/debounceAsync/index.test.ts b/packages/debounceAsync/index.test.ts
index 77a5578..f07c4a3 100644
--- a/packages/debounceAsync/index.test.ts
+++ b/packages/debounceAsync/index.test.ts
@@ -34,20 +34,20 @@ describe('debounceAsync', () => {
     jest.useFakeTimers();
     const rawFn = jest.fn(someAsyncTask);
     const debounced = debounceAsync(rawFn, 10);
-    const cb = jest.fn();
+    const resolveOrReject = jest.fn();
     new Array(5).fill(0).map((_, i) =>
       debounced(i * 2, 10, i % 2 === 0)
-        .then(cb)
-        .catch(cb),
+        .then(resolveOrReject)
+        .catch(resolveOrReject),
     );
 
     expect(rawFn).not.toHaveBeenCalled();
-    expect(cb).not.toHaveBeenCalled();
+    expect(resolveOrReject).not.toHaveBeenCalled();
     jest.advanceTimersByTime(500);
     await flushPromises();
     expect(rawFn).toHaveBeenCalledTimes(1);
     expect(rawFn).lastCalledWith(8, 10, true);
-    expect(cb).toHaveBeenCalledTimes(1);
-    expect(cb).lastCalledWith(8);
+    expect(resolveOrReject).toHaveBeenCalledTimes(1);
+    expect(resolveOrReject).lastCalledWith(8);
   });
 });