# Testing Stores — Redux Toolkit / Zustand

Source: https://www.skillbyai.com/en/redux-zustand/z-test

> Reset state between tests.

## Test actions as plain functions

Because stores are module singletons, state leaks between tests unless you reset it. Capture the initial state once and call `setState(initial, true)` (replace mode) in `beforeEach`. Test actions directly through `getState()` without rendering, and test components with React Testing Library against the real store. The Zustand docs also describe a test-framework mock of `zustand` that resets every store automatically after each test; check the docs for the version matching your test runner. For Redux, create a fresh store per test with `configureStore` so tests are independent.

## Vitest tests for the cart store

Reset, act, assert.

```typescript
import { beforeEach, describe, expect, it } from 'vitest';
import { useCart } from './cartStore';

const initial = useCart.getState();

beforeEach(() => {
  useCart.setState(initial, true); // replace, do not merge
});

describe('cart store', () => {
  it('adds a new item with qty 1', () => {
    useCart.getState().add('sku-1');
    expect(useCart.getState().items).toEqual([{ id: 'sku-1', qty: 1 }]);
  });

  it('increments an existing item', () => {
    useCart.getState().add('sku-1');
    useCart.getState().add('sku-1');
    expect(useCart.getState().items[0].qty).toBe(2);
  });

  it('starts empty in every test', () => {
    expect(useCart.getState().items).toHaveLength(0);
  });
});
```

## Resetting a chessboard

Before every practice game you put all the pieces back on their starting squares; otherwise the next game starts from a position nobody planned.

**Quiz:** Why call setState(initial, true) in beforeEach?

- [ ] To speed up rendering
- [x] To restore a clean store so tests do not leak state into each other
- [ ] To enable devtools in tests
- [ ] To persist state between test files

*Answer:* To restore a clean store so tests do not leak state into each other. Module-level stores keep their state across tests otherwise.