effect-vitest

Entry Point

import { it, expect } from "@effect/vitest"

Feature	Description
it.effect	Injects TestContext (includes TestClock)
it.live	Uses live Effect environment (real clock, logging)
it.scoped	Provides a Scope for resource management
it.scopedLive	Combines scoped + live
it.flakyTest	Retries flaky tests until success or timeout

Basic Tests

import { it, expect } from "@effect/vitest"
import { Effect } from "effect"

it.effect("test success", () =>
  Effect.gen(function* () {
    const result = yield* Effect.succeed(42)
    expect(result).toBe(42)
  })
)

Testing Failures with Exit

import { it, expect } from "@effect/vitest"
import { Effect, Exit } from "effect"

it.effect("test failure", () =>
  Effect.gen(function* () {
    const result = yield* Effect.exit(Effect.fail("oops"))
    expect(result).toStrictEqual(Exit.fail("oops"))
  })
)

TestClock

it.effect provides TestClock starting at 0. Use it.live for real time.

import { it } from "@effect/vitest"
import { Clock, Effect, TestClock } from "effect"

it.effect("with simulated time", () =>
  Effect.gen(function* () {
    yield* TestClock.adjust("1000 millis")
    const now = yield* Clock.currentTimeMillis
    // now === 1000
  })
)

it.live("with real time", () =>
  Effect.gen(function* () {
    const now = yield* Clock.currentTimeMillis
    // now === actual system time
  })
)

Scoped Tests

Use it.scoped when your test acquires resources.

import { it } from "@effect/vitest"
import { Console, Effect } from "effect"

const resource = Effect.acquireRelease(
  Console.log("acquire"),
  () => Console.log("release")
)

it.scoped("manages resources", () =>
  Effect.gen(function* () {
    yield* resource // automatically released after test
  })
)

Flaky Tests

import { it } from "@effect/vitest"
import { Effect, Random } from "effect"

const flaky = Effect.gen(function* () {
  if (yield* Random.nextBoolean) return yield* Effect.fail("random failure")
})

it.effect("retry until success", () =>
  it.flakyTest(flaky, "5 seconds")
)

Test Modifiers

it.effect.skip("skipped test", () => Effect.void)
it.effect.only("run only this", () => Effect.void)
it.effect.fails("expected to fail", () => Effect.fail("expected"))

Logging

Logging is suppressed in it.effect. Enable with custom logger or it.live:

import { it } from "@effect/vitest"
import { Effect, Logger } from "effect"

it.effect("with logging", () =>
  Effect.log("visible").pipe(Effect.provide(Logger.pretty))
)

it.live("logging enabled by default", () =>
  Effect.log("visible")
)