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');
}