testing.mdx

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Testing	How to test your new store	9

Resetting state between tests in react-dom

When running tests, the stores are not automatically reset before each test run.

Thus, there can be cases where the state of one test can affect another. To make sure all tests run with a pristine store state, you can mock zustand during testing and use the following code to create your store:

import { create as actualCreate } from 'zustand'
// const actualCreate = jest.requireActual('zustand') // if using jest
import { act } from 'react-dom/test-utils'

// a variable to hold reset functions for all stores declared in the app
const storeResetFns = new Set()

// when creating a store, we get its initial state, create a reset function and add it in the set
export const create = (createState) => {
  const store = actualCreate(createState)
  const initialState = store.getState()
  storeResetFns.add(() => store.setState(initialState, true))
  return store
}

// Reset all stores after each test run
beforeEach(() => {
  act(() => storeResetFns.forEach((resetFn) => resetFn()))
})

The way you mock a dependency depends on your test runner/library.

In jest, you can create a __mocks__/zustand.js and place the code in that file. If your app is using zustand/vanilla instead of zustand, then you'll have to place the above code in __mocks__/zustand/vanilla.js.

TypeScript usage

If you are using zustand, as documented in TypeScript Guide, use the following code:

import { create as actualCreate, StateCreator } from 'zustand'
// const actualCreate = jest.requireActual('zustand') // if using jest
import { act } from 'react-dom/test-utils'

// a variable to hold reset functions for all stores declared in the app
const storeResetFns = new Set<() => void>()

// when creating a store, we get its initial state, create a reset function and add it in the set
export const create =
  () =>
  <S,>(createState: StateCreator<S>) => {
    const store = actualCreate<S>(createState)
    const initialState = store.getState()
    storeResetFns.add(() => store.setState(initialState, true))
    return store
  }

// Reset all stores after each test run
beforeEach(() => {
  act(() => storeResetFns.forEach((resetFn) => resetFn()))
})

Resetting state between tests in react-native and jest

You should use the following code in the __mocks__/zustand.js file (the __mocks__ directory should be adjacent to node_modules, placed in the same folder as node_modules, unless you configured roots to point to a folder other than the project root jest docs: mocking node modules):

import { act } from '@testing-library/react-native'
const actualCreate = jest.requireActual('zustand')

// a variable to hold reset functions for all stores declared in the app
const storeResetFns = new Set()

// when creating a store, we get its initial state, create a reset function and add it in the set
const create = (createState) => {
  const store = actualCreate.default(createState)
  const initialState = store.getState()
  storeResetFns.add(() => {
    store.setState(initialState, true)
  })
  return store
}

// Reset all stores after each test run
beforeEach(async () => {
  await act(() =>
    storeResetFns.forEach((resetFn) => {
      resetFn()
    })
  )
})

export default create

If the jest.config.js has automock: false, then you need to do the following in jest.setup.js:

jest.mock('zustand')