How to run same test multiple times using jest

Question

I am using jest to run my test suite (with back-end as Node.js & express). Below is my code:

const puppeteer = require ('puppeteer');

test('testing login function', async () => {
    const browser = await puppeteer.launch ({  
        headless: true,
        args: ['--no-sandbox']
  });

    const page = await browser.newPage();

    await page.type('#username', 'admin');
    await page.type('#password', 'password');

    await page.click('login-button');

    await page.waitFor('.card');

    expect(texthead).toEqual('Welcome to webpage');

    await browser.close();
});

I am trying to run this same test multiple times at once, is there a way using it by jest, or maybe using other tools.

Yes, I tried for loop but it will run sequentially. I want to run multiple tests at once. — Arghajeet Bhattacharya
– Arghajeet Bhattacharya, Commented Sep 13, 2018 at 19:08

mbelsky · Accepted Answer · 2022-11-07 14:00:57Z

40

If you're looking for something that will essentially stress test a single test (looking for test flakiness like I was) then you could use the following one-liner in your terminal, which of course uses bash and Jest together.

for i in {1..100}; do npx jest <test_file> --silent || (echo "Failed after $i attempts" && break); done

This specific command requires you to have npx installed and it uses the --silent option but you can change it as you please.

edited Nov 7, 2022 at 14:00

mbelsky

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answered May 1, 2019 at 14:28

Brady Dowling

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2 Comments

Moshisho Over a year ago

A useful flag in jest for this case would be -o (instead of <test_file>). Run only modified/new tests that way you can have "Flakiness CI" on your tests.

Russ Hyde Over a year ago

When running this with a failing test, I get the following printed Failed after $i attempts bash: break: only meaningful in a for', while', or until' loop` and the loop doesn't break. An alternative is

for i in {1..100}; do npx jest <test_file> --silent; if [[ "$?" != 0 ]]; then echo "Failed after $i attempts" && break; fi; done

. The double quotes are needed to interpolate $i

Ohhh · Accepted Answer · 2023-04-10 17:06:03Z

23

Jest has a built in method for this using .each(). https://jestjs.io/docs/api#testeachtablename-fn-timeout

If you want to change the parameters of each test, you can pass an array of test parameters to .each([1,2,3]). If this is un-necessary, just fill the array with null.

test.each(Array(100).fill(null))('may be flaky test', async () => {})

This can optionally be run in parallel using .concurrent test.concurrent.each(Array(100).fill(null))('may be flaky test', async () => {})

answered Apr 10, 2023 at 17:06

Ohhh

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Comments

Herman Starikov · Accepted Answer · 2018-09-13 20:04:42Z

6

If you don't want tests run sequentially, you can use Promise.all. Here is a quick example of how you could refactor your code.

const runTheTest = async () => { 
  const browser = await puppeteer.launch ({
    headless: true, args: ['--no-sandbox'] 
  });
  .......
  return browser.close();
}

test('testing login function', async () => { 
  const testRuns = []
  for (let index = 0; index < NUMBER_OF_RUNS; index++) {
    testRuns.push(runTheTest())
  }
  return Promise.all(testRuns);
})

answered Sep 13, 2018 at 20:04

Herman Starikov

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Comments

gqstav · Accepted Answer · 2021-08-10 09:33:26Z

3

npx installed packages over and over and I wanted to time if my change improved the test speed. It's not great, but what I did was putting a command in the package.json

"jest": "jest <file_path> --silent"

and then borrowed the script from Brady as

for i in {1..100}; do yarn jest || (echo 'Failed after $i attempts' && break); done

I wrapped it in a timer, but that's not necessary really.

answered Aug 10, 2021 at 9:33

gqstav

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1 Comment

Rafał Cieślak Over a year ago

(echo 'Failed after $i attempts' && break) is going to execute in a subshell and break will exit that subshell, not the actual loop. This can be fixed by using curly braces instead: {echo "Failed after $i attempts" && break}

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