@johngw/stream/test/transformers/reduce.test.ts

Reactive programming tools using the WHATWG Streams API.

import { fromTimeline } from '@johngw/stream-jest'
import { reduce } from '@johngw/stream/transformers/reduce'
import { write } from '@johngw/stream/sinks/write'

test('accumulates values from a stream', async () => {
  await expect(
    fromTimeline<number>(`
    -0-1-2-3-4-|
  `).pipeThrough(
      reduce({} as Record<string, number>, (acc, chunk) => ({
        ...acc,
        [chunk.toString()]: chunk,
      }))
    )
  ).toMatchTimeline(`
    -----------{0: 0,1: 1,2: 2,3: 3,4: 4}-
  `)
})

test('flushing', async () => {
  await expect(
    fromTimeline<number>(`
    -0-1-2-3------------------4-5-|
  `).pipeThrough(
      reduce(
        {} as Record<string, number>,
        (acc, chunk) => ({
          ...acc,
          [chunk.toString()]: chunk,
        }),
        {
          flushes: fromTimeline(`
    ----------null----------------|
        `),
        }
      )
    )
  ).toMatchTimeline(`
    ----------{0: 0,1: 1,2: 2,3: 3}---{0: 0,1: 1,2: 2,3: 3,4: 4,5: 5}-
  `)
})

test('allow flush errors to be sent down stream', async () => {
  await expect(
    fromTimeline<number>(`
    ----|
  `)
      .pipeThrough(
        reduce(0, (acc, x) => acc + x, {
          flushes: fromTimeline(`
    --E-|
          `),
        })
      )
      .pipeTo(write())
  ).rejects.toThrow()
})

test('disallow flush errors to be sent down stream', async () => {
  await expect(
    fromTimeline<number>(`
    -0-1-2---3-4-5-|
  `).pipeThrough(
      reduce(0, (acc, x) => acc + x, {
        ignoreFlushErrors: true,
        flushes: fromTimeline(`
    -------E-------|
        `),
      })
    )
  ).toMatchTimeline(`
    ---------------15-
  `)
})