Jest and recurring actions

Sometimes you want to have Jest perform a recurring action between each task.

Some examples: Query a database, clear storage, clear mocked data, or reset a mocked route.

We don't really want to be bothered with having this recurring code in each test, and luckily Jest has a solution for us.

Recurring actions

There are four functions we can hook into:

beforeEach: Runs before each test
afterEach: Runs after each test
beforeAll: Runs before all tests
afterAll: Runs after all tests

Let's sketch an example. We have a database function to call, so the steps we want to achieve are:

create database
populate with mock data
re-populate for each test
remove database

This scenario is a perfect case for all four functions to hook into.

The first thing we want is to create our database, for which we'll use the beforeAll function.

beforeAll(() => {
  return createDatabase();
});

The next step is to populate the database with demo data we can alter in our tests.

beforeEach(() => {
  return populateDatabase();
});

Our test might alter/remove/create elements in this database, so we want to clear it between each test.

afterEach(() => {
  return clearDatabase();
});

And once we are all done, we should remove the database so the next run will be fresh again.

afterAll(() => {
  return removeDatabase();
});

And that's it, these four steps will now run at the needed times. To showcase this, let's create this sample test file and see when each call is used.

test('user database has Chris', () => {
  expect(db.user.hasName('Chris')).toBeTruthy();
});

test('user database doesnt have Thomas', () => {
  expect(db.user.hasName('Thomas')).not.toBeTruthy();
});

The firing order is as follows:

beforeAll: Created the database
beforeEach: Populates database
Test 1 runs: Find user Chris
afterEach: Clear database
beforeEach: Populates database
Test 2 runs: Can't find Thomas
afterEach: Clear database
afterAll: Remove database

And that's the flow it will take.

We can quickly make our test more manageable and work in specific ways to ensure each test is solid and fresh.

Thank you for reading, and let's connect!

Thank you for reading my blog. Feel free to subscribe to my email newsletter and connect on Facebook or Twitter

Jest and recurring actions

Comments

More from this blog

I wrote 1000 articles, what’s next?

Vendure community and more

Deploying Vendure

Vendure - Overwriting email templates

Customizing vendure

Recurring actions

Thank you for reading, and let's connect!

Command Palette

Comments

More from this blog

Recurring actions

Thank you for reading, and let's connect!