Testing a React/Redux Toolkit app with Typescript

This article is based on Up & Running with React, Redux Toolkit, Typescript and React Router. If you haven't check that out yet, please go skim through this article first.

If you have no idea about testing in react, you might wanna check that one as well. Test your React components and APIs with React Testing Library, Jest, Typescript, and Axios

Working Example

If you've done component testing before, but you have no idea about how to test the components connected to Redux Toolkit(RTK) or slices then you are in the right place. Today we test our reduxified
components and slice reducers. For components, we'll put ourselves in user's shoes and will think and act like them. So, we are not going to test our components, but rather test the functionalities of them.
By doing this, we'll have a holistic view of our app, and we'll be able to see if everything integrates smoothly with each other.

For slices, we'll test them in an isolated environment(as units), supply them with their ActionPayloads accordingly and see if it really adds, edits or deletes.

Technologies we'll dabbling with will be Typescript, RTK, React Router and React Testing Library(RTL). Since testing UI and UI related
things always sounds scary I'll try to smoothen this proccess as much as I can. Buckle up.

Project structure:

├─ src
│ ├─ App.tsx
│ ├─ components
│ │ ├─ BookInfo.tsx
│ │ └─ Navbar.tsx
│ ├─ hooks
│ │ └─ index.ts
│ ├─ index.tsx
│ ├─ logo.svg
│ ├─ pages
│ │ ├─ AddBook.tsx
│ │ └─ BookList.tsx
│ ├─ react-app-env.d.ts
│ ├─ redux
│ │ ├─ bookSlice.ts
│ │ └─ store.ts
│ ├─ reportWebVitals.ts
│ ├─ setupTests.ts
│ ├─ types.d.ts
│ └─ tests
│ │ ├─ reduxComponent.spec.tsx
│ │ ├─ reduxUnitTests.spec.ts

Before we go any further, first let's update some components from the previous article.

bookSlice.ts

import { createSlice, PayloadAction } from '@reduxjs/toolkit';
import { RootState } from './store';
import { BookState } from '../types';

type initialStateType = {
  bookList: BookState[],
};

const bookList: BookState[] = [
  {
    id: '1',
    title: '1984',
    author: 'George Orwell',
  },
  {
    id: '2',
    title: "Harry Potter and the Philosopher's Stone",
    author: 'J. K. Rowling',
  },
  {
    id: '3',
    title: 'The Lord of the Rings',
    author: 'J.R.R Tolkien',
  },
];

const initialState: initialStateType = {
  bookList,
};

export const bookSlice = createSlice({
  name: 'book',
  initialState,
  reducers: {
    addNewBook: (state, action: PayloadAction<BookState>) => {
      state.bookList.push(action.payload);
    },
    updateBook: (state, action: PayloadAction<BookState>) => {
      const {
        payload: { title, id, author },
      } = action;

      state.bookList = state.bookList.map((book) =>
        book.id === id ? { ...book, author, title } : book,
      );
    },
    deleteBook: (state, action: PayloadAction<{ id: string }>) => {
      state.bookList = state.bookList.filter((book) => book.id !== action.payload.id);
    },
  },
});

export const { addNewBook, updateBook, deleteBook } = bookSlice.actions;

export const selectBookList = (state: RootState) => state.book.bookList;

export default bookSlice.reducer;

I've updated ids of initalState, previously it was uuid() which was getting generated randomly. But we need a constant id for testing. I usually make a fixture file to
place those constant variables, but I did not want to make things complicated.

AddBook.tsx

<Heading color="white" data-testid="header">
  {id ? 'Update Book' : 'Add Book'}
</Heading>

I've changed the title to conditional render, so we can check if we are on the add or update page.

That was all the changes. Let's start testing our bookSlice.

Testing Slice

reduxUnitTests.spec.ts

import { store } from '../redux/store';
import { deleteBook, updateBook, addNewBook } from '../redux/bookSlice';

test('Updates a books author and title', () => {
  let state = store.getState().book;
  const unchangedBook = state.bookList.find((book) => book.id === '1');
  expect(unchangedBook?.title).toBe('1984');
  expect(unchangedBook?.author).toBe('George Orwell');

  store.dispatch(updateBook({ id: '1', title: '1985', author: 'George Bush' }));
  state = store.getState().book;
  let changeBook = state.bookList.find((book) => book.id === '1');
  expect(changeBook?.title).toBe('1985');
  expect(changeBook?.author).toBe('George Bush');

  store.dispatch(updateBook({ id: '1', title: '1984', author: 'George Orwell' }));
  state = store.getState().book;
  const backToUnchangedBook = state.bookList.find((book) => book.id === '1');

  expect(backToUnchangedBook).toEqual(unchangedBook);
});

test('Deletes a book from list with id', () => {
  let state = store.getState().book;
  const initialBookCount = state.bookList.length;

  store.dispatch(deleteBook({ id: '1' }));
  state = store.getState().book;

  expect(state.bookList.length).toBeLessThan(initialBookCount); // Checking if new length smaller than inital length, which is 3
});

test('Adds a new book', () => {
  let state = store.getState().book;
  const initialBookCount = state.bookList.length;

  store.dispatch(addNewBook({ id: '4', author: 'Tester', title: 'Testers manual' }));
  state = store.getState().book;
  const newlyAddedBook = state.bookList.find((book) => book.id === '4');
  expect(newlyAddedBook?.author).toBe('Tester');
  expect(newlyAddedBook?.title).toBe('Testers manual');
  expect(state.bookList.length).toBeGreaterThan(initialBookCount);
});

We got three different test cases:

Updating a book with given author, title and id.
Deleting a book with a given id
Adding a book with given author, title and id

In test Updates a books author and title, we fetch bookList state from store, then we find the book with the id of 1, and then since we already know id 1 book is 1984 and the author is George Orwell
we check that if it's true.

Then, we dispatch(updateBook({ id: '1', title: '1985', author: 'George Bush' })); and check again with new values. Then convert it back to first state to check against original
state.

In test Deletes a book from list with id, all we do is dispatch a delete action with id and check initialLength and updatedLength if updatedLength is lower than ìnitial
we are good to go.

In test Adds a new book, we dispatch add action, then check for newly added values and finally checking initialLength and updatedLength to see if new length is greater.

Testing Reduxified Component

import {
  render,
  screen,
  fireEvent,
  RenderResult,
} from '@testing-library/react';
import { Provider } from 'react-redux';
import BookInfo from '../components/BookInfo';
import AddBook from '../pages/AddBook';
import { Route, MemoryRouter } from 'react-router-dom';

import { store } from '../redux/store';
import { BookState } from '../types';

const renderBook = (book: BookState): RenderResult =>
  render(
    <Provider store={store}>
      <BookInfo title={book.title} author={book.author} id={book.id} />
    </Provider>
  );

const renderAddBook = (): RenderResult =>
  render(
    <Provider store={store}>
      <MemoryRouter>
        <AddBook />
      </MemoryRouter>
    </Provider>
  );

const renderUpdateBook = (id: string): RenderResult =>
  render(
    <Provider store={store}>
      <MemoryRouter initialEntries={[`/update-book/${id}`]}>
        <Route path="/update-book/:id">
          <AddBook />
        </Route>
      </MemoryRouter>
    </Provider>
  );

const getABook = (bookId: string): BookState => {
  const book = store
    .getState()
    .book.bookList.find((book) => book.id === bookId);
  expect(book).not.toBeUndefined();
  return book as BookState;
};



test('Renders BookInfo', () => {
  const book = getABook('1');
  renderBook(book);
  expect(screen.getByText('1984')).toHaveTextContent('1984');
});



test('AddBook page', () => {
  renderAddBook();
  const initialLength = store.getState().book.bookList.length;

  let titleInput = screen.getByPlaceholderText('The Lord of the Rings'); // Since we know placeholder is already The Lord of the Rings so we can query by it
  expect(titleInput).toBeInTheDocument();
  fireEvent.change(titleInput, { target: { value: 'Test Title' } });
  expect(titleInput).toHaveValue('Test Title');

  let authorInput = screen.getByPlaceholderText('J.R.R Tolkien'); // Since we know placeholder is already J.R.R Tolkien
  expect(authorInput).toBeInTheDocument();
  fireEvent.change(authorInput, { target: { value: 'Test Author' } });
  expect(authorInput).toHaveValue('Test Author');

  let submitButton = screen.getByText('Submit');
  fireEvent.click(
    submitButton,
    new MouseEvent('click', {
      bubbles: true,
      cancelable: true,
    })
  );

  let book = store.getState().book.bookList.length;
  expect(book).toBeGreaterThan(initialLength);
});



test('UpdateBook page', () => {
  const bookId = '1';
  renderUpdateBook(bookId);
  let updateBookData = getABook(bookId);

  const updateBookText = screen.getByTestId('header');
  expect(updateBookText).toHaveTextContent('Update Book');

  let titleInput = screen.getByDisplayValue(updateBookData!.title!); //Making sure by finding titleInput with prepopulated title
  expect(titleInput).toBeInTheDocument();
  fireEvent.change(titleInput, { target: { value: 'Test Title' } }); //And changing its data
  expect(titleInput).toHaveValue('Test Title');

  let authorInput = screen.getByDisplayValue(updateBookData!.author!); //Making sure by finding authorInput with prepopulated author

  expect(authorInput).toBeInTheDocument();
  fireEvent.change(authorInput, { target: { value: 'Test Author' } }); //And changing its data
  expect(authorInput).toHaveValue('Test Author');

  let submitButton = screen.getByText('Submit');
  fireEvent.click(
    submitButton,
    new MouseEvent('click', {
      bubbles: true,
      cancelable: true,
    })
  );

  updateBookData = getABook(bookId);
  expect(updateBookData.title).toBe('Test Title'); // Checking the book with id=1 now has Test Title
  expect(updateBookData.author).toBe('Test Author'); // Checking the book with id=1 now has Test Author
});

Before we begin tests, we need to make our utility functions renderAddBook, renderUpdateBook, renderBook and getABook. In renderUpdateBook and renderAddBook
we've used Memory Router to test our React Router as well.

Our first test Renders BookInfo, renders a book with the id of 1, which is 1984 all we have to do check whether there is an element associated with 1984 or not.

In test AddBook page, we first fetch our input fields by placeholders since they are already defined we can easily access it. Then we fireEvent to fill them up, then as if it's real user, we press submit button, and finally like we've previously done in slice we check bookList's length to see if it incremented.

In test UpdateBook page, this one is pretty similar to AddBook page, but we first fetch book id that comes from useParams if it's really there, we know we would have
prepopulated input fields with associated id information in our case it's 1984 and George Orwell. And we know if we are updating, title should be Update Book we also check
that one as well. Then we can values of fields and trigger submit button click like we do earlier, and finally checking the id=1 is really has title of Test Title and author of Test Author.

Now if you are done all you have to do yarn test. We now have a working test suite. They will keep running as you are working,
and they will constantly check your code against test cases in case anything breaks.

Thanks for reading 🥳🥳🥳.

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