jest-zest

Shorter and more readable tests in jest. Combines TypeScript and Proxy.

import { lazy, freshFn, vary } from 'jest-zest';
import { render } from '@testing-library/react';
import user from '@testing-library/user-event';
import '@testing-library/jest-dom';

// `freshFn` creates many jest.fn() that are mock.mockClear() after every test.
const [onAddComment, onEditPost] = freshFn;
// `vary` lets you redefine a value with nested describes, useful for given-when-then tests.
const userKind = vary('normal');
// `lazy` uses Proxy to lazily perform render() whose result is cached within each test run.
// We destructure `getByRole` and `queryByRole` which also Proxy to the underlying method.
const { getByRole, queryByRole } = lazy(() =>
  render(
    <Page
      userKind={userKind()}
      onAddComment={onAddComment}
      onEditPost={onEditPost}
    />
  )
);

it('shows add comment button', () => {
  expect(getByRole('button', { name: 'Add comment' })).toBeVisible();
});

it('hides edit post button', () => {
  expect(queryByRole('button', { name: 'Edit post' })).toBeNull();
});

describe('when add comment is clicked', () => {
  beforeEach(() => {
    user.click(getByRole('button', { name: 'Add comment' }));
  });

  it('calls onAddComment', () => {
    expect(onAddComment).toHaveBeenCalledTimes(1);
  });
});

describe('when user is admin', () => {
  new userKind('admin');

  it('shows edit post button', () => {
    expect(getByRole('button', { name: 'Edit post' })).toBeVisible();
  });

  describe('when edit post is clicked', () => {
    beforeEach(() => {
      user.click(getByRole('button', { name: 'Edit post' }));
    });

    it('calls onEditPost', () => {
      expect(onEditPost).toHaveBeenCalledTimes(1);
    });
  });
});

userKind.each(['admin', 'editor'])('when user is %s', () => {
  it('shows edit post button', () => {
    expect(getByRole('button', { name: 'Edit post' })).toBeInTheDocument();
  });

  describe('when edit post is clicked', () => {
    beforeEach(() => {
      user.click(getByRole('button', { name: 'Edit post' }));
    });

    it('calls onEditPost', () => {
      expect(onEditPost).toHaveBeenCalledTimes(1);
    });
  });
});

Documentation

lazy(creator: () => T, cleanup?: (object?: T) => void)

Pass a creator function that will be called lazily yet only once. Run cleanup callback for each test via afterEach().

Before:

import { render } from '@testing-library/react';
import user from '@testing-library/user-event';

const subject = () => render(<CreatePostForm />);

it('shows a form', () => {
  expect(subject().getAllByRole('form')).toHaveLength(1);
});

it('shows content input', () => {
  const { getAllByRole, getByLabelText } = subject();
  expect(getAllByRole('textbox')).toContain(getByLabelText('Content'));
});

it('shows post button', () => {
  expect(subject().getByRole('button', { name: 'Post' })).toBeInTheDocument();
});

it('disables post button', () => {
  expect(subject().getByRole('button', { name: 'Post' })).toBeDisabled();
});

describe('when user types content', () => {
  let result: typeof ReturnType<subject>;
  beforeEach(() => {
    result = subject();
    return user.type(result.getByLabelText('Content'), 'New content');
  });

  it('enables the post button', () => {
    expect(result.getByRole('button', { name: 'Post' })).toBeEnabled();
  });
});

After:

import { render } from '@testing-library/react';

const { getByRole, getAllByRole, getByLabelText } = lazy(() =>
  render(<CreatePostForm />)
);
const postButton = lazy(() => getByRole('button', { name: 'Post' }));

it('shows a form', () => {
  expect(getAllByRole('form')).toHaveLength(1);
});

it('shows content input', () => {
  expect(getAllByRole('textbox')).toContain(getByLabelText('Content'));
});

it('shows post button', () => {
  expect(postButton()).toBeInTheDocument();
});

it('disables post button', () => {
  expect(postButton()).toBeDisabled();
});

describe('when content is added', () => {
  beforeEach(() => user.type(getByLabelText('Content'), 'New content'));

  it('enables the post button', () => {
    expect(postButton()).toBeDisabled();
  });
});

freshFn

Can be called or destructured to create a new jest.fn() that is clearer with mockClear() after each test run.

Before:

const onChange = jest.fn();
const onFocus = jest.fn();
const onBlur = jest.fn();

afterEach(() => {
  onChange.mockClear();
  onFocus.mockClear();
  onBlur.mockClear();
});

const props = {
  onChange,
  onFocus,
  onBlur,
};

After by calling:

import { freshFn } from 'jest-zest';

const props = {
  onChange: freshFn(),
  onFocus: freshFn(),
  onBlur: freshFn(),
};

After by destructuring:

import { freshFn } from 'jest-zest';

const [onChange, onFocus, onBlur] = freshFn;
const props = {
  onChange,
  onFocus,
  onBlur,
};

fresh(creator: () => T, refresher: (object: T) => void)

Create multiple of something that must be cleared for each test. Great for spies like jest.fn().

It accepts two arguments:

1. Pass a function that will be called initially to create your object
2. A function that clears the object using afterEach()

To then create an instance, either:

• call it to create a single instance
• destructure it like an array to create multiple instances

Before:

const onChange = jest.fn();
const onFocus = jest.fn();
const onBlur = jest.fn();

afterEach(() => {
  onChange.mockClear();
  onFocus.mockClear();
  onBlur.mockClear();
});

After:

import { fresh } from 'jest-zest';

const [onChange, onFocus, onBlur] = fresh(jest.fn, mock => mock.mockClear());

vary()

Define and redefine a value shared between tests easily.

Before:

let variation: string;

function subject() {
  return render(<Component variation={variation} />);
}

describe('when variation is orange', () => {
  beforeEach(() => {
    variation = 'orange';
  });

  it('shows text orange', () => {
    expect(subject().getByText('orange')).toBeInTheDocument();
  });
});

describe('when variation is blue', () => {
  beforeEach(() => {
    variation = 'blue';
  });

  it('shows text blue', () => {
    expect(subject().getByText('blue')).toBeInTheDocument();
  });
});

After:

const color = vary('');
const subject = lazy(() => render(<Component color={color()} />));

describe('when color is orange', () => {
  new color('orange');

  it('shows text orange', () => {
    expect(subject.getByText('orange')).toBeInTheDocument();
  });
});

describe('when color is blue', () => {
  new color('blue');

  it('shows text blue', () => {
    expect(subject.getByText('blue')).toBeInTheDocument();
  });
});