subscribe.js

const GanacheCore = require('ganache-core')
const pify = require('pify')

module.exports = (test, testLabel, SubscribeBlockTracker) => {

  test(`${testLabel} - latest`, async (t) => {
    const provider = GanacheCore.provider()
    const blockTracker = new SubscribeBlockTracker({
      provider,
    })

    try {
      t.equal(blockTracker.isRunning(), false, 'SubscribeBlockTracker should begin stopped')

      const blocks = []
      blockTracker.on('latest', (block) => blocks.push(block))
      t.equal(blockTracker.isRunning(), true, 'SubscribeBlockTracker should start after listener is added')
      t.equal(blocks.length, 0, 'no blocks so far')

      await newLatestBlock(blockTracker)
      t.equal(blocks.length, 1, 'saw 1st block')

      const latestBlock = newLatestBlock(blockTracker)
      await triggerNextBlock(provider)
      await latestBlock
      t.equal(blocks.length, 2, 'saw 2nd block')

      await triggerNextBlock(provider)
      await triggerNextBlock(provider)
      const lastBlockPromise = newLatestBlock(blockTracker)
      await triggerNextBlock(provider)
      const lastBlock = await lastBlockPromise
      t.equal(blocks.length, 5, 'saw all intermediate blocks')
      t.equal(Number.parseInt(lastBlock, 16), 4, 'saw correct block, with number 4')

      blockTracker.removeAllListeners()
      t.equal(blockTracker.isRunning(), false, 'SubscribeBlockTracker stops after all listeners are removed')

    } catch (err) {
      t.ifError(err)
    }

    // cleanup
    blockTracker.removeAllListeners()
    t.end()
  })

}

async function triggerNextBlock (provider) {
  await pify((cb) => provider.sendAsync({ id: 1, method: 'evm_mine', jsonrpc: '2.0', params: [] }, cb))()
}

async function newLatestBlock (blockTracker) {
  return await pify(blockTracker.once, { errorFirst: false }).call(blockTracker, 'latest')
}