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

Reactive programming tools using the WHATWG Streams API.

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

test('only emits distinct values', async () => {
  await expect(
    fromTimeline(`
    -1-1-2-2-2-1-2-3-4-3-2-1-|
    `).pipeThrough(distinct())
  ).toMatchTimeline(`
    -1---2---------3-4--------
  `)
})

test('selecting a distinct key', async () => {
  await expect(
    fromTimeline<{ a: number; n: string }>(`
    -{a: 4,n: f}-{a: 7,n: b}-{a: 5,n: f}-|
    `).pipeThrough(distinct({ selector: (x) => x.n }))
  ).toMatchTimeline(`
    -{a: 4,n: f}-{a: 7,n: b}-----------|
  `)
})

test('flushing with a stream', async () => {
  await expect(
    fromTimeline(`
    -1-1------1-1-|
    `).pipeThrough(
      distinct({
        flushes: fromTimeline(`
    -----N---------
        `),
      })
    )
  ).toMatchTimeline(`
    -1---1---------
  `)
})

test('allow flush errors to be sent down stream', async () => {
  await expect(
    fromTimeline(`
    -------------X
    `)
      .pipeThrough(
        distinct({
          flushes: fromTimeline(`
    -E------------
    `),
        })
      )
      .pipeTo(write())
  ).rejects.toThrow('Timeline Error')
})

test('disallow flush errors to be sent down stream', async () => {
  await expect(
    fromTimeline(`
    -1-1------1-1-|
    `).pipeThrough(
      distinct({
        ignoreFlushErrors: true,
        flushes: fromTimeline(`
    -----E---------
        `),
      })
    )
  ).toMatchTimeline(`
    -1-------------
  `)
})