First things first, create a project in Supabase. Once you've got that set up, head over to the settings->API section in your Supabase dashboard. There, you'll find the SUPABASE_URL and SUPABASE_SERVICE_KEY. Keep these handy, you'll need them later for configuring the connection in your Jest tests.

Next up, let's get Jest installed in your project folder. You can use npm or yarn for this.

# with npm
npm install jest

# with yarn
yarn add jest

Now, let's initialize Jest. Run the following command to create a new Jest config file.

npx jest --init

During the setup, you can choose to use Typescript, pick the environment, and tweak other settings based on what your project needs.

You'll need Supabase-js to interact with Supabase in your code, and dotenv to load environment variables.

# with npm
npm install @supabase/supabase-js dotenv

# with yarn
yarn add @supabase/supabase-js dotenv

Create a .env file at the root of your project and add the Supabase URL and service key you got earlier.

SUPABASE_URL=your-supabase-url
SUPABASE_SERVICE_KEY=your-supabase-service-key

Don't forget to add .env to your .gitignore file. You don't want to accidentally share sensitive data.

Time to create an instance of the Supabase client. You can put this in a separate file and then import it into your test files.

require('dotenv').config()
const { createClient } = require('@supabase/supabase-js')

const supabaseUrl = process.env.SUPABASE_URL
const supabaseKey = process.env.SUPABASE_SERVICE_KEY
const supabase = createClient(supabaseUrl, supabaseKey)

module.exports = supabase

Now, let's write some tests using Jest. You can use the Supabase client to call your Supabase API in your tests.

const supabase = require('./supabase')

describe('Supabase tests', () => {
  it('should return all users', async () => {
    const { data, error } = await supabase
      .from('users')
      .select('*')

    expect(error).toBeNull()
    expect(Array.isArray(data)).toBeTruthy()
    expect(data.length).toBeGreaterThan(0)
  })
})

And there you have it! With these steps, you should be all set to use Supabase with Jest for testing. Happy coding!