0.5.0 • Public • Published

NoFlo component/graph testing and embedding wrapper

Wraps a component to provide a convenient interface for use in normal JavaScript code. It is compatible with any testing paradigm: TDD/BDD/whatever. Read also Embedding NoFlo.


  • Provides easy JavaScript access to long-running NoFlo graphs
  • Reduces boilerplate to set up a component testbed.
  • Provides common high-level methods.
  • Provides low-level access to the component, ports and events.
  • Compatible with different testing frameworks and complex test cases.

Getting started

Install noflo-wrapper and add it to your project's dependecies:

npm install noflo-wrapper --save

Require it:

const Wrapper = require('noflo-wrapper');

Use methods described below and run the tests just as you do it normally with your favorite testing framework.


Explanations below contain examples in JavaScript using Mocha and Chai in BDD style. You can also write your tests using any other framework or style.

Loading a component

First you need to create a new Wrapper object to wrap your component or graph:

const t = new Wrapper('my-noflo-app/Multiplier');

The constructor accepts either a full component name (including namespace prefix), or a function returning an instantiated component object, or a NoFlo Graph instance.

In general, components are loaded and wired up asynchronously, so you need to start the wrapper like this (and resolve the Promise) before running any tests:

before(() => t.start());

Advanced options

If the component to be tested is a NoFlo graph, you can pass custom event handlers to the Wrapper constructor:

const t = new Wrapper('my-noflo-app/Multiplier', {
  load: (err, instance) => {
    // This is called after loading the graph
  ready: (err, instance) => {
    // This is called when the network is ready to be attached

Sending inputs and expecting output

A high-level receive method listens on output ports for data and groups until a disconnect event.

A high-level send methods sends data followed by a disconnect to one or more input ports.

Here is an example that tests a simple multiplier component:

t.receive('xy', (data) => {

  x: 5,
  y: 6,

Note that receive is called before send, because it binds event handlers asynchronously, while send is almost an instant operation.

Short syntax for send method to send data and disconnect to just one inport looks like this:

t.send('x', 123);

Direct access to component, ports and events

In more complex test cases you might want to send IPs and handle particular events manually:

t.outs.xy.on('data', (data) => {


Wrapper object provides ins and outs hashmaps of sockets attached to the component.

You can also access the NoFlo network directly via network property:

if ( {
  // Do something

Receiving multiple data chunks and groups

As receive is triggered by a disconnect event, there might be multiple data packets in the transmission and also some group bracket IPs. In such case they are available as arrays and counts in the callback arguments:

t.receive('xy', (data, groups, dataCount, groupCount) => {
  chai.expect(data).to.eql([4, 10, 18]);
  chai.expect(groups).to.eql(['foo', 'bar']);

Note that groupCount counts only closed groups via endGroup events, while groups contains unique groups sent to the output.

Receiving from multiple output ports

If a component sends output to multiple ports at the same time and you need to test results from all of them at once, that may require some syncrhonization spaghetti in your specs. But receive simplifies it by accepting a hashmap and returning a Promise that is resolved when results from all outputs in the map have been received:

let div = null;
let mod = null;

  quotient: (data) => {
    div = data;
  remainder: (data) => {
    mod = data;
  .then(() => {
    chai.expect(div).to.equal 3
    chai.expect(mod).to.equal 2

  dividend: 11,
  divisor: 3,

Using promises to chain subsequent receives

The receive method returns a Promise resolved when a transmission is received, so you can chain subsequent transmissions in a thenable way, e.g.:

t.receive('quotient', (data) => {
  .then(() => {
    t.receive('quotient', (data) =>
      dividend: 56,
      divisor: 7,
  dividend: 30,
  divisor: 6,

Capturing Flowtraces

noflo-wrapper supports capturing Flowtraces for your runs. This enables retroactive debugging of the data flow in tools like Flowhub.

You can enable this with:

const t = new Wrapper('my-noflo-app/Multiplier', {
  debug: true,

If you want to manage your own Flowtraces, you can also pass in an instance instead:

const { Flowtrace } = new Flowtrace();
const myTrace = new Flowtrace();
const t = new Wrapper('my-noflo-app/Multiplier', {
  flowtrace: myTrace,

Under Node.js you can save the captured Flowtrace into a file with:

const tracefile = await t.dumpTrace();

If you want to store it some other way, it can be accessed via t.tracer.


See complete BDD-style examples in spec folder.


The first thing to start developing this package is:

npm install

Then run bundled Mocha specs:

npm test

Then feel free to hack on the lib and specs.


  • 0.5.0 (2020-12-10)
    • Wrapper start method now returns a Promise when no callback is provided
    • Added compatibility with NoFlo 1.4 Promises API
  • 0.4.1 (2020-11-27)
    • Fixed an issue with subgraph networks transmitting IIPs twice
  • 0.4.0 (2020-11-26)
    • Now using the new Flowtrace functionality in NoFlo 1.3
    • Wrapper can now also wrap noflo.Graph objects
  • 0.3.0 (2020-09-14)
    • Ported from CoffeeScript to ES6
    • Now using native Promises instead of Bluebird



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