diff --git a/src/store/middleware/autoSyncMiddleware.test.ts b/src/store/middleware/autoSyncMiddleware.test.ts
new file mode 100644
index 0000000..f92b3d3
--- /dev/null
+++ b/src/store/middleware/autoSyncMiddleware.test.ts
@@ -0,0 +1,112 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+
+import { AutoSyncManager } from './autoSyncMiddleware'
+
+const { syncToFlaskBulkMock } = vi.hoisted(() => ({
+  syncToFlaskBulkMock: vi.fn(() => ({ type: 'sync/bulk' })),
+}))
+
+vi.mock('../slices/syncSlice', () => ({
+  syncToFlaskBulk: syncToFlaskBulkMock,
+  checkFlaskConnection: vi.fn(() => ({ type: 'sync/check' })),
+}))
+
+const nextTick = () => new Promise(resolve => setTimeout(resolve, 0))
+
+const waitFor = async (assertion: () => void, attempts = 5) => {
+  let lastError: unknown
+
+  for (let i = 0; i < attempts; i += 1) {
+    await nextTick()
+
+    try {
+      assertion()
+      return
+    } catch (error) {
+      lastError = error
+    }
+  }
+
+  throw lastError
+}
+
+const createControlledPromise = () => {
+  let resolve: () => void
+
+  const promise = new Promise<void>((resolvePromise) => {
+    resolve = resolvePromise
+  })
+
+  return {
+    promise,
+    resolve: resolve!,
+  }
+}
+
+describe('AutoSyncManager', () => {
+  let manager: AutoSyncManager
+  let dispatchMock: ReturnType<typeof vi.fn>
+
+  beforeEach(() => {
+    manager = new AutoSyncManager()
+    dispatchMock = vi.fn()
+    manager.setDispatch(dispatchMock)
+    syncToFlaskBulkMock.mockClear()
+  })
+
+  afterEach(() => {
+    vi.useRealTimers()
+  })
+
+  it('serializes performSync calls', async () => {
+    const firstSync = createControlledPromise()
+    dispatchMock
+      .mockReturnValueOnce(firstSync.promise)
+      .mockResolvedValueOnce(undefined)
+
+    const firstRun = manager.syncNow()
+    const secondRun = manager.syncNow()
+
+    await waitFor(() => {
+      expect(dispatchMock).toHaveBeenCalledTimes(1)
+    })
+
+    firstSync.resolve()
+    await Promise.all([firstRun, secondRun])
+
+    expect(dispatchMock).toHaveBeenCalledTimes(2)
+  })
+
+  it('resets changeCounter after a successful sync', async () => {
+    dispatchMock.mockResolvedValue(undefined)
+
+    manager.trackChange()
+    manager.trackChange()
+
+    await manager.syncNow()
+
+    expect(manager.getStatus().changeCounter).toBe(0)
+  })
+
+  it('runs one pending sync after an in-flight sync finishes', async () => {
+    const firstSync = createControlledPromise()
+    dispatchMock
+      .mockReturnValueOnce(firstSync.promise)
+      .mockResolvedValueOnce(undefined)
+
+    const syncPromise = manager.syncNow()
+
+    await waitFor(() => {
+      expect(dispatchMock).toHaveBeenCalledTimes(1)
+    })
+
+    manager.trackChange()
+    manager.trackChange()
+
+    firstSync.resolve()
+    await syncPromise
+    await waitFor(() => {
+      expect(dispatchMock).toHaveBeenCalledTimes(2)
+    })
+  })
+})
diff --git a/src/store/middleware/autoSyncMiddleware.ts b/src/store/middleware/autoSyncMiddleware.ts
index 2c77491..e6ac92c 100644
--- a/src/store/middleware/autoSyncMiddleware.ts
+++ b/src/store/middleware/autoSyncMiddleware.ts
@@ -10,7 +10,7 @@ interface AutoSyncConfig {
   maxQueueSize: number
 }
 
-class AutoSyncManager {
+export class AutoSyncManager {
   private config: AutoSyncConfig = {
     enabled: false,
     intervalMs: 30000,