Load testing with RxJS

_RxJSTesting.md

This script spins up a number of agents (default 4), each with a certain average timeBetweenActions (default 400msec), and it uses a Poisson process in order to keep that average timeBetweenActions, but randomly distributed within that constraint. Think - popcorn popping!

This statistical trick is a valid model of random arrivals of users at a website, and will distribute load nicely. Thanks to the live-updating progress indicators of ascii-progress, and the awesome stream-fu provided by RxJS!

Here's a short video of my thoughts on the matter: https://www.youtube.com/watch?v=0GnB8FAJjfY

loadtest.js

import Rx from 'rxjs'
import ProgressBar from 'ascii-progress'

/* Test config */
const numAgents = 4
const numActionsPerAgent = 12
const timeBetweenActions = 400
const agentOffset = timeBetweenActions / numAgents

/* Run test ! */
let agents = Rx.Observable
    .range(0, numAgents)

let work = agents
    .map(i => ({
        index: i,
        progress: new ProgressBar({
            schema: ':bar :current/:total :percent :elapseds :etas',
            total: numActionsPerAgent,
            blank: '◦',
            filled: '●'
        })
    })).mergeMap(({ index, progress }) => {
        // every agent gets turned into a stream that
        return Rx.Observable.concat(
            // begins with an offset delay
            Rx.Observable.timer(index * agentOffset),
            // then proceeds with #numActionsPerAgent actions
            Rx.Observable
                .range(0, numActionsPerAgent)
                // spaced out by on average timeBetweenActions, but with some jitter
                .concatMap(() =>
                    // add some random jitter around timeBetweenActions
                    Rx.Observable.timer(-Math.log(1.0 - Math.random()) * timeBetweenActions)
                )
                // and ticking on each one
                .do(() => {
                    /*
                        TODO insert real work here (if async, place the tick() inside a then() block)
                    */
                    progress.tick()
                })
        )
    })

work.subscribe({
    complete() {
        /* Show results and exit */
        console.log('Tests pass YAY!')
        process.exit(0)
    },
    error(e) {
        console.log(e)
        process.exit(1)
    }
})