test/parallel/test-zlib-flush-drain.js

'use strict';
require('../common');
const assert = require('assert');
const zlib = require('zlib');

const bigData = Buffer.alloc(10240, 'x');

const opts = {
  level: 0,
  highWaterMark: 16
};

const deflater = zlib.createDeflate(opts);

// shim deflater.flush so we can count times executed
let flushCount = 0;
let drainCount = 0;

const flush = deflater.flush;
deflater.flush = function(kind, callback) {
  flushCount++;
  flush.call(this, kind, callback);
};

deflater.write(bigData);

const ws = deflater._writableState;
const beforeFlush = ws.needDrain;
let afterFlush = ws.needDrain;

deflater.flush(function(err) {
  afterFlush = ws.needDrain;
});

deflater.on('drain', function() {
  drainCount++;
});

process.once('exit', function() {
  assert.strictEqual(
    beforeFlush, true);
  assert.strictEqual(
    afterFlush, false);
  assert.strictEqual(
    drainCount, 1);
  assert.strictEqual(
    flushCount, 1);
});