trying to understand how to run an effect in the background, provided as a layer to another program

effect-in-layer.ts

import * as F from '@effect-ts/core/Effect/Fiber'
import * as L from '@effect-ts/core/Effect/Layer'
import * as M from '@effect-ts/core/Effect/Managed'
import * as T from '@effect-ts/core/Effect'
import { pipe } from '@effect-ts/core/Function'
import { tag } from '@effect-ts/core/Has'
import { testRuntime } from '@effect-ts/jest/Runtime'

describe('run an effect forever in the background and stop when the test is done', () => {

  const log: string[] = []

  interface LogForeverFiber {
    fiber: F.Fiber<never, never>
  }

  const LogForeverFiber = tag<LogForeverFiber>()

  // in real application this would drain a queue
  const logForever = pipe(
    T.succeedWith(() => {
      log.push('log')
    }),
    T.delay(400),
    T.forever,
  )

  // fork logForever into a new fiber when program starts,
  // interrupt the fiber when the program ends
  const LogForeverFiberLive = pipe(
    logForever,
    T.fork,
    M.makeInterruptible(F.interrupt),
    M.map((fiber): LogForeverFiber => ({ fiber })),
    L.fromManaged(LogForeverFiber)
  )

  const { it } = testRuntime(LogForeverFiberLive)

  // fails, log is empty
  it('works', () => T.gen(function* (_) {
    yield* _(T.delay(2000)(T.unit))
    expect(log).toEqual([
      'log',
      'log',
      'log',
      'log',
      'log',
    ])
  }))

})