feat: support type inference with a new `test.extend` syntax #9550

sheremet-va · 2026-01-29T15:21:41Z

Description

TODO

Fix errors in rolldown

This PR adds new test.extend syntax that supports type inference:

import { test as baseTest } from 'vitest'

const test = baseTest
  .extend('config', { scope: 'worker' }, async () => {
    return { port: 3000, host: 'localhost' }
  })
  .extend('database', { scope: 'file' }, async ({ config }, { onCleanup }) => {
    const db = new Database(`${config.host}:${config.port}`)
    await db.connect()

    onCleanup(async () => {
      await db.disconnect()
    })

    return db
  })
  .extend('user', async ({ database }) => {
    return await database.createTestUser()
  })

test('user is created in database', async ({ user, database }) => {
  // TypeScript knows:
  // - user is the return type of createTestUser()
  // - database is Database
  const found = await database.findUser(user.id)
  expect(found).toEqual(user)
})

Fixes #9305
Fixes #9555

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sheremet-va · 2026-01-29T15:22:05Z

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docs/guide/test-context.md

test/cli/test/scoped-fixtures.test.ts

hi-ogawa

The API looks better to me than use magic. It still delegates to use mechanism internally, but I like it.
I haven't look what's going to happen in next PR #9553

docs/guide/test-context.md

test/core/test/fixture-initialization.test.ts

sheremet-va · 2026-01-30T19:21:10Z

test/cli/test/scoped-fixtures.test.ts

  }, { globals: true })
-  expect(stdout).toContain('basic.test.ts')
-  expect(stderr).toBe('')
+  expect(stderr).toMatchInlineSnapshot(`


This is a breaking change, but it simplifies mental model A LOT. Scoped fixtures can only use other scoped fixtures with a higher scope, and scope is explicit (but overriding the fixture also inherits all the options by default, like in PW).

By default, any extended value has a test scope. You cannot override the extended value to provide a DIFFERENT scope, it now throws an error. This is needed to remove the ambiguity of defining a worker fixture and then overriding its "static" dependency inside the suite:

// this worked previously const test = base .extend('port', 5300) .extend('config', { scope: 'worker' }, ({ port }) => { return `localhost:${port}` })

But if you want to override the port, you need to invalidate or overwrite the WORKER fixture that we already initialized - which makes little sense

test.override('port', 5000) // what to do here?

Using test.override with a scope other than test in general is now forbidden, unless it's called at the top level of the file (which still causes some unexpected issues with worker fixtures because they will leak to other test files in the same worker - I wonder if we could force a new worker instead).

This also makes it so you cannot call test.extend('', { scope: 'file' }) inside a suite, it's only allowed in the top level of the module now

I wasn't checking these test cases previously and the new extend/override behavior makes sense to me.

sheremet-va · 2026-01-30T19:24:13Z

@hi-ogawa I updated the fixtures inheritance (there is now a TestFixters class that tracks test's fixtures), please take a look. I am also introducing a small breaking change, not sure if we can put it into 4.1, but the impact should be small, I believe (I could probably implement it with backwards compatibility if we are ok with small bugs)

sheremet-va · 2026-01-30T19:34:50Z

test/cli/test/around-each.test.ts

-    >> db fixture teardown
-    >> aroundEach teardown"
+    >> aroundEach teardown
+    >> db fixture teardown"


This behaviour seems to make more sense than what was here before because you should be able to access db after calling runTest(). Previously the db was torn down by that point 🤔

Right, this looks like what I suggested to happen in #9450 (comment) I forgot to double check the test.

sheremet-va · 2026-01-30T21:27:20Z

Damn it, snapshots fail on rolldown because it processes files differently 😡

sheremet-va · 2026-01-30T21:28:31Z

docs/guide/test-context.md

+
+By default, fixtures are initialized for each test. You can change this with the `scope` option to share fixtures across tests.
+
+::: warning


Added this warning section, @hi-ogawa. Would love to know what you think

The behavior looks reasonable to me. Note sure "force a new worker" behavior is better.

I think "force a new worker" is what playwright does, otherwise worker fixtures ovrerride each other in different files

hi-ogawa

TestFixtures class looks great.

hi-ogawa · 2026-01-31T03:10:17Z

packages/runner/src/map.ts

 }

-export function getTestFixture<Context = TestContext>(key: Context): FixtureItem[] {
+export function getTestFixturesManager<Context = TestContext>(key: Context): TestFixtures {


nit: any reason renaming only getTestFixture -> getTestFixturesManager but keeping setTestFixture?

That was one of the old attempts, I reverted to TestFixtures. There are now fixtures (the instance of the class) that have registrations

hi-ogawa · 2026-01-31T03:25:31Z

packages/runner/src/fixture.ts

+  }
+
+  extend(runner: VitestRunner, userFixtures: Record<string, any>): TestFixtures {
+    const { suite } = getCurrentSuite()


nit: TestFixtures structure looks great, but TestFixtures.extend/override relying on getCurrentSuite feels odd in terms of state separation. How about pass it from argument?

I did pass it before, but moved it into the function directly in the last commit. We already call this function inside withFixtures anyway. The suite collection is intentionally global and fixture values rely on what suite they are in, so they are inherently tied. If we had a separate Runner class that does the collection, then it would make sense

hi-ogawa · 2026-01-31T03:45:48Z

test/cli/test/around-each.test.ts

-    >> db fixture teardown
-    >> aroundEach teardown"
+    >> aroundEach teardown
+    >> db fixture teardown"


Right, this looks like what I suggested to happen in #9450 (comment) I forgot to double check the test.

hi-ogawa · 2026-01-31T03:51:45Z

test/cli/test/scoped-fixtures.test.ts

  }, { globals: true })
-  expect(stdout).toContain('basic.test.ts')
-  expect(stderr).toBe('')
+  expect(stderr).toMatchInlineSnapshot(`


I wasn't checking these test cases previously and the new extend/override behavior makes sense to me.

sheremet-va force-pushed the 01-29-feat_support_type_inference_with_new_test.extend_syntax branch 3 times, most recently from 4f3ae6f to af1c234 Compare January 29, 2026 18:02

sheremet-va requested a review from hi-ogawa January 29, 2026 18:02

sheremet-va marked this pull request as ready for review January 29, 2026 18:03

sheremet-va added this to the 4.1.0 milestone Jan 29, 2026

sheremet-va force-pushed the 01-29-feat_support_type_inference_with_new_test.extend_syntax branch 3 times, most recently from b2c0ea8 to cf27bce Compare January 29, 2026 18:14

sheremet-va mentioned this pull request Jan 29, 2026

feat: provide context to beforeAll, afterAll and aroundAll hooks #9553

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sheremet-va changed the title ~~feat: support type inference with new test.extend syntax~~ feat: support type inference with a new test.extend syntax Jan 29, 2026

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sheremet-va force-pushed the 01-29-feat_support_type_inference_with_new_test.extend_syntax branch 3 times, most recently from 45fe275 to c3a889c Compare January 30, 2026 19:10

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sheremet-va force-pushed the 01-29-feat_support_type_inference_with_new_test.extend_syntax branch from c3a889c to 225e631 Compare January 30, 2026 19:33

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feat: support type inference with new test.extend syntax

a85eea4

sheremet-va force-pushed the 01-29-feat_support_type_inference_with_new_test.extend_syntax branch from 3d73ede to a85eea4 Compare January 30, 2026 21:26

sheremet-va commented Jan 30, 2026

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hi-ogawa reviewed Jan 31, 2026

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refactor: cleanup, review

5f3c003

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		By default, fixtures are initialized for each test. You can change this with the `scope` option to share fixtures across tests.

		::: warning

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feat: support type inference with a new test.extend syntax #9550

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feat: support type inference with a new `test.extend` syntax #9550

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