@electric-sql/d2mini/tests/graph.test.ts

D2Mini is a minimal implementation of Differential Dataflow for performing in-memory incremental view maintenance.

import { describe, expect, beforeEach, test } from 'vitest'
import { DifferenceStreamReader, DifferenceStreamWriter } from '../src/graph.js'
import { MultiSet } from '../src/multiset.js'

describe('DifferenceStreamReader and DifferenceStreamWriter', () => {
  let writer: DifferenceStreamWriter<number>
  let reader: DifferenceStreamReader<number>

  beforeEach(() => {
    writer = new DifferenceStreamWriter<number>()
    reader = writer.newReader()
  })

  test('isEmpty returns true for empty queue', () => {
    expect(reader.isEmpty()).toBe(true)
  })

  test('isEmpty returns false when queue has messages', () => {
    writer.sendData(new MultiSet())
    expect(reader.isEmpty()).toBe(false)
  })

  test('drain returns all messages', () => {
    writer.sendData(new MultiSet([[1, 1]]))
    writer.sendData(new MultiSet([[2, 1]]))

    const messages = reader.drain()
    expect(messages).toHaveLength(2)
    expect(messages[0]).toBeInstanceOf(MultiSet)
    expect(messages[1]).toBeInstanceOf(MultiSet)
    expect(reader.isEmpty()).toBe(true)
  })

  test('multiple readers receive the same data', () => {
    const reader2 = writer.newReader()

    writer.sendData(new MultiSet([[1, 1]]))
    writer.sendData(new MultiSet([[2, 1]]))

    const messages1 = reader.drain()
    const messages2 = reader2.drain()

    expect(messages1).toHaveLength(2)
    expect(messages2).toHaveLength(2)
    expect(messages1[0].getInner()).toEqual([[1, 1]])
    expect(messages2[0].getInner()).toEqual([[1, 1]])
    expect(messages1[1].getInner()).toEqual([[2, 1]])
    expect(messages2[1].getInner()).toEqual([[2, 1]])
  })

  test('drain empties the queue', () => {
    writer.sendData(new MultiSet([[1, 1]]))
    writer.sendData(new MultiSet([[2, 1]]))

    expect(reader.isEmpty()).toBe(false)
    reader.drain()
    expect(reader.isEmpty()).toBe(true)
  })
})