Sharing data between test suites.

[alanskovrlj]

car.js

const car = new Car()

export function getCar() { return car }

test-file1.js

import { getCar } from './car.js'

test-file2.js

import { getCar } from './car.js'

In javascript when you import instance of a class in multiple places, you will get that same instance because of module caching. Because vitest uses worker threads and runs each test file separately every import is a new instance. What is the recommended approach for sharing an instance or any other variables across multiple vitest test files?

[AriPerkkio]

What is the recommended approach for sharing an instance or any other variables across multiple vitest test files?

That's not recommended at all. All test files should be isolated from each other and work without each other.

[alanskovrlj]

Ok, but what would be my options for sharing state if I wanna go non recommended way? Think of it as I'm just breaking a large test file into multiple and they all depend on a external operation which I would like to perfom only once and share that state between all of them.

[AriPerkkio]

You could try isolate: false but I think even then the modules are reset between the test files:

vitest/packages/vitest/src/runtime/runBaseTests.ts

Lines 56 to 60 in a12ec00

	for (const file of files) {
	if (isolate) {
	executor.mocker.reset()
	resetModules(workerState.moduleCache, true)
	}

With provide you can share serializable state from main thread, but even then there's no way to update it from inside the test runner / test files.

[AriPerkkio]

external operation which I would like to perfom only once and share that state between all of them

Actually this sounds exactly like the use case for global setup and then passing the result to test runners with provide.

[alanskovrlj]

Provide functionality kinda works because it allows me to prepare some serializable data beforehand and inject it, but what I would really want is to pass this class instance down to test files and call it whenever, but maybe I'm just trying to shoot myself in foot with this anyway, so I think I'll go with this approach 😄. Thanks!