How do I manually configure Shards for execution

[mvgiacomello]

In a project I am working on, we use vitest to drive Puppeteer tests. These tests take a lot of resources to run and we know which ones can be run in parallel and which can only run alone in our CI. Is there a way to manually configure which tests run in parallels and which in sequence? Basically manually defining the shards.

We tried the following without much success :

// Import tests ABCDEF which are async functions with `test()` and `test.concurrent()` inside.

suite('Test Suite', async () => {
  describe.concurrent('Group A', async () => {
    describe('testA', testA)
    describe('testB', testB)
    describe('testC, testC)
  })
  describe('testD', testD)
  describe.concurrent('Group B', async () => {
    describe('testE', testE)
    describe('testF', testF)
  })
})

We're also using the configs:

minWorkers: 1
maxWorkers: 2

[hi-ogawa]

One potential confusion is that test.concurrenty is configured by maxConcurrency https://vitest.dev/config/#maxconcurrency and minWorkers/maxWorkers is for configuring test-file based concurrency.

For example, if you have multiple test files, which should run one by one, and then in each file, you want to use test.concurrency but concurrent up to 2, then probably this config would do it:

• minWorkers = maxWorkers = 1
• maxConcurrency = 2

---

Btw, you didn't mention in which way it's not working. Is it too serial? or is it too concurrent?

We tried the following without much success :

[mvgiacomello]

Humm, thanks @hi-ogawa - okay, so I was missing the maxConcurrency in my config file. That should solve part of my problems.

Btw, you didn't mention in which way it's not working

Going back to my main question. I'd like to set maxWorkers=2 so I could run 2 files in parallel, however, I'd like to specifically tell vitest which files are okay to run in parallel as some tests are quite heavy to run together.

[hi-ogawa]

I'd like to set maxWorkers=2 so I could run 2 files in parallel, however, I'd like to specifically tell vitest which files are okay to run in parallel as some tests are quite heavy to run together.

I don't think that's currently possible with a single vitest command.
Probably you would need to split to two test commands, something like:

{
  "test:light": "vitest --exclude '**/*.heavy.test.ts' --maxWorkers 2"
  "test:heavy": "vitest '.heavy.test.ts' --maxWorkers 1"
}

Or these two patterns are distinct enough, then you could prepare two configs:

{
  "test:light": "vitest -c vitest.config.light.ts"
  "test:heavy": "vitest -c vitest.config.heavy.ts"
}

[mvgiacomello]

Thank you very much, @hi-ogawa, the first suggestion did the job! 👏