Best Practices for Implementing Redux Mock Store in Your Projects

Redux mock store is a library designed to test the asynchronous and synchronous actions of a Redux store without interacting with the actual store. It provides a mock store for your tests with the same API as a real Redux store, but with simplified capabilities that allow you to assert on the actions that have been dispatched. This is particularly useful for unit tests where you want to ensure that the correct actions are being dispatched under certain conditions.

Copy
1import configureMockStore from 'redux-mock-store';
2const mockStore = configureMockStore();
3const store = mockStore({ myState: 'sample state' });

Benefits of Using a Redux Mock Store

Using a redux mock store simplifies the testing process by allowing developers to focus on the behavior of the actions and reducers without worrying about the state changes in the actual redux store. It also helps in ensuring that components are correctly dispatching actions and that the store is updated as expected.

Setting Up Your Environment

Importing Necessary Libraries

To start writing tests with redux mock store, you need to import react, the testing library, and other necessary libraries. These imports set the stage for creating a mock store and writing your tests.

Copy
1import React from 'react';
2import { Provider } from 'react-redux';
3import configureMockStore from 'redux-mock-store';

Installing redux-mock-store

To install the redux-mock-store library, you can use npm or yarn. This will add the library to your project's dependencies, allowing you to create a configured mock store.

Copy
1npm install redux-mock-store --save-dev

Creating a Redux Mock Store

Configuring the Mock Store

To configure the mock store, you typically create a function that initializes it with the desired middlewares and initial state. This configured mock store can then be used throughout your test files.

Copy
1import configureMockStore from 'redux-mock-store';
2import thunk from 'redux-thunk';
3
4const middlewares = [thunk];
5const mockStore = configureMockStore(middlewares);
6
7const initialState = {};
8const store = mockStore(initialState);

Generating a Store Instance

When you need a new store instance for a test, you can call the mock store function with an optional initial state. This instance will be used to dispatch actions and test the state of the store.

Copy
1const store = mockStore({ myState: 'initial state' });

Writing Tests with Redux Mock Store

Mocking Redux Store in React Testing Library

To mock Redux store in the React Testing Library, you can use the Provider component to wrap your react components. This allows you to pass the mock store instance as the store prop, ensuring that the component has access to the store during the test.

Copy
1import { render } from '@testing-library/react';
2import { Provider } from 'react-redux';
3
4const store = mockStore({ myState: 'initial state' });
5
6const customRender = (ui, options) =>
7  render(ui, { wrapper: ({ children }) => <Provider store={store}>{children}</Provider>, ...options });
8
9// Use customRender instead of render in your tests

Testing Reducers with Mock Store

Unit testing reducers with a mock store involves dispatching actions and checking if the reducer updates the state as expected. This is a straightforward process since reducers are pure functions.

Copy
1import reducer from 'myReducer';
2import * as types from 'actionTypes';
3
4describe('reducer', () => {
5  it('should handle SOME_ACTION', () => {
6    expect(
7      reducer({}, {
8        type: types.SOME_ACTION,
9        payload: 'some data',
10      })
11    ).toEqual({ ...expectedState });
12  });
13});

Complex Test Combining Actions and Reducers

For a complex test combining actions, you can dispatch multiple actions to the mock store and then assert the final state. This type of integration test verifies that the action creators and reducers work together correctly.

Copy
1describe('complex actions', () => {
2  it('should execute multiple actions', () => {
3    const store = mockStore({ myState: 'initial' });
4
5    store.dispatch(someActionCreator());
6    store.dispatch(anotherActionCreator());
7
8    const actions = store.getActions();
9    expect(actions).toEqual([...expectedActions]);
10    expect(store.getState()).toEqual(expectedFinalState);
11  });
12});

Integrating Redux Mock Store with Custom Render Function

Implementing Your Own Custom Render Function

Creating your own custom render function allows you to include additional context providers or setup that is common across multiple tests. This function wrapper helps to avoid repetitive code and maintain consistency.

Copy
1import { render as rtlRender } from "@testing-library/react";
2import { createStore } from "redux";
3import { Provider } from "react-redux";
4// import your reducers and initial state
5import rootReducer from "./reducers";
6import { initialState } from "./store";
7
8function render(
9  ui,
10  {
11    initialState,
12    store = createStore(rootReducer, initialState),
13    ...renderOptions
14  } = {}
15) {
16  function Wrapper({ children }) {
17    return <Provider store={store}>{children}</Provider>;
18  }
19  return rtlRender(ui, { wrapper: Wrapper, ...renderOptions });
20}
21
22// re-export everything
23export * from "@testing-library/react";
24// override render method
25export { render };

With this custom render function, you can now easily render your react components in a testing environment that includes your redux store. This is particularly useful when you have a connected component that relies on the redux store state or dispatches actions.

For example, when testing a connected component, you can use your own custom render function like this:

Copy
1import { render, screen } from "my-test-utils";
2// assuming you exported your custom render function as 'render'
3import MyConnectedComponent from "./MyConnectedComponent";
4
5test("renders with redux", () => {
6  render(<MyConnectedComponent />);
7  expect(screen.getByText(/some text/i)).toBeInTheDocument();
8});

This setup ensures that your component is tested within the context of a redux Provider store, making it possible to test both the component's behavior and its interaction with the redux store.

Wrapping Components with Provider Store

To ensure that your react components have access to the mock store during testing, you can wrap them with the Provider component from react-redux. This provider store makes the Redux store available to any nested components that have been wrapped in the connect() function.

Copy
1import { Provider } from 'react-redux';
2import { render } from '@testing-library/react';
3import MyConnectedComponent from './MyConnectedComponent';
4import configureMockStore from 'redux-mock-store';
5
6const mockStore = configureMockStore();
7const store = mockStore({ myState: 'initial state' });
8
9const wrapper = ({ children }) => <Provider store={store}>{children}</Provider>;
10
11const { getByTestId } = render(<MyConnectedComponent />, { wrapper });
12
13expect(getByTestId('component-id')).toBeTruthy();

Testing Asynchronous Actions

Handling Async Actions with Redux Mock Store

Testing asynchronous actions requires a redux mock store configured with middleware like redux-thunk. This allows you to write tests that handle asynchronous logic within your action creators.

Copy
1import configureMockStore from 'redux-mock-store';
2import thunk from 'redux-thunk';
3import { fetchSomeData } from './actions';
4
5const middlewares = [thunk];
6const mockStore = configureMockStore(middlewares);
7
8it('creates SUCCESS when fetching data has been done', () => {
9  const expectedActions = [
10    { type: 'REQUEST' },
11    { type: 'SUCCESS', payload: { data: 'some data' } }
12  ];
13  const store = mockStore({ data: [] });
14
15  return store.dispatch(fetchSomeData()).then(() => {
16    expect(store.getActions()).toEqual(expectedActions);
17  });
18});

Writing Tests for Thunk Actions

When writing tests for thunk actions, you can use the async and await keywords to wait for the promise to resolve. This ensures that all the dispatched actions are accounted for in your tests.

Copy
1import configureMockStore from 'redux-mock-store';
2import thunk from 'redux-thunk';
3import * as actions from './actionCreators';
4
5const middlewares = [thunk];
6const mockStore = configureMockStore(middlewares);
7
8it('handles async action creators', async () => {
9  const store = mockStore({ data: null });
10  const expectedActions = [
11    { type: 'LOAD_DATA_REQUEST' },
12    { type: 'LOAD_DATA_SUCCESS', payload: { data: 'some async data' } }
13  ];
14
15  await store.dispatch(actions.loadData());
16  expect(store.getActions()).toEqual(expectedActions);
17});

Verifying Dispatched Actions

Capturing All the Dispatched Actions

To verify that your redux mock store is dispatching actions as expected, you can use the getActions method. This method returns an array of all the actions that have been dispatched to the store instance during the test.

Copy
1it('should dispatch the correct actions', () => {
2  const store = mockStore({ data: [] });
3
4  store.dispatch({ type: 'ACTION_ONE' });
5  store.dispatch({ type: 'ACTION_TWO' });
6
7  const actions = store.getActions();
8  expect(actions).toEqual([{ type: 'ACTION_ONE' }, { type: 'ACTION_TWO' }]);
9});

Analyzing the Action Log

The action log provided by the getActions method can be used to analyze the dispatched actions inside your tests. This allows you to ensure that the correct actions are being dispatched and in the right order.

Copy
1it('should dispatch actions in the correct order', () => {
2  const store = mockStore({ data: [] });
3
4  store.dispatch({ type: 'FIRST_ACTION' });
5  store.dispatch({ type: 'SECOND_ACTION' });
6
7  const actions = store.getActions();
8  expect(actions[0].type).toBe('FIRST_ACTION');
9  expect(actions[1].type).toBe('SECOND_ACTION');
10});

Advanced Mocking Techniques

Mocking an RTK Query

When using Redux Toolkit, you may need to mock an RTK query for your tests. This involves creating a mock store and dispatching the async thunk action created by the RTK query.

Copy
1import { configureStore } from '@reduxjs/toolkit';
2import { usersApi } from './services/users';
3
4const store = configureStore({
5  reducer: {
6    [usersApi.reducerPath]: usersApi.reducer,
7  },
8  middleware: (getDefaultMiddleware) =>
9    getDefaultMiddleware().concat(usersApi.middleware),
10});
11
12it('mocks an RTK query', async () => {
13  const result = await store.dispatch(usersApi.endpoints.getUser.initiate(1));
14  expect(result.data).toEqual({ id: 1, name: 'John Doe' });
15});

ClearActions Clears the Action Log

After each test, it's a good practice to clear the action log to ensure that subsequent tests start with a clean slate. The clearActions method resets the store's dispatched actions array inside, making it ready for a new test.

Copy
1it('clears the action log between tests', () => {
2  const store = mockStore({ data: [] });
3
4  store.dispatch({ type: 'ACTION_ONE' });
5  expect(store.getActions()).toEqual([{ type: 'ACTION_ONE' }]);
6
7  store.clearActions();
8  expect(store.getActions()).toEqual([]);
9});

Best Practices for Testing Redux

Structuring Test Code for Readability

When writing tests, it's important to structure your test code in a way that is easy to read and understand. Using describe blocks to group related tests and it or test for individual test cases can help organize your test code effectively.

Copy
1describe('actions', () => {
2  describe('action creators', () => {
3    it('should create an action to add a todo', () => {
4      const expectedAction = {
5        type: 'ADD_TODO',
6        text: 'Finish docs'
7      };
8      expect(actions.addTodo('Finish docs')).toEqual(expectedAction);
9    });
10  });
11});

Keeping Tests Focused on Action Related Logic

It's crucial to keep your tests focused on the action related logic. This means that each test should only assert the outcomes of specific actions or sequences of actions, rather than testing multiple pieces of logic at once.

Copy
1it('should handle adding a todo', () => {
2  const store = mockStore({ todos: [] });
3
4  store.dispatch(addTodo('Run tests'));
5
6  const actions = store.getActions();
7  const expectedPayload = { type: 'ADD_TODO', text: 'Run tests' };
8  expect(actions).toEqual([expectedPayload]);
9});

Debugging Tests Using Redux Mock Store

Inspecting the State and Dispatched Actions Inside Tests

When a test fails, you may need to inspect the state and dispatched actions to understand what went wrong. Logging the state and actions can provide valuable insights during the debugging process.

Copy
1it('should update the state correctly', () => {
2  const store = mockStore({ items: [] });
3
4  store.dispatch(addItem('New Item'));
5  console.log(store.getState()); // Log the state for debugging
6  console.log(store.getActions()); // Log the dispatched actions
7
8  expect(store.getState().items).toContain('New Item');
9});

Troubleshooting Common Issues with Mock Store

Common issues with using redux mock store in tests include actions not being dispatched as expected or the state not updating correctly. To troubleshoot, ensure that your mock store is properly configured and that you're using the correct assertions.

Copy
1it('should dispatch actions correctly', () => {
2  const store = mockStore({ loading: false });
3
4  store.dispatch(startLoading());
5  store.dispatch(stopLoading());
6
7  const expectedActions = [
8    { type: 'START_LOADING' },
9    { type: 'STOP_LOADING' }
10  ];
11
12  expect(store.getActions()).toEqual(expectedActions);
13});

By following these guidelines and using the provided code examples, you can effectively use redux mock store to test your Redux logic. Remember to keep your tests focused, structured, and maintain a clear separation between testing different parts of your Redux code. With practice, you'll become proficient at writing tests that help ensure the reliability and maintainability of your Redux applications.