Procmonrest

A promise-based child process monitor to ensure reliable testing of local servers written in JS.

This project adheres to the standard coding style (click below for more information):

Raison d'être

I wanted to create a set of reliable, end-to-end tests for a REST API that I was working on. In order to do this, I decided to write some code that would start up the server in an entirely separate process, and monitor its stdout to see when it was ready to accept requests. This worked out so well that I started replicating the code across projects, and, of course, that's when it should become an npm module.

Getting started

Install via NPM:

npm install procmonrest --save-dev

Or Yarn:

yarn add procmonrest --dev

Then create a new instance of Procmonrest and wait for the start() method to resolve before running your tests. Afterwards, wait for the stop() method to resolve before continuing on to the next test suite, or the next step in your build process.

For example (using mocha):

import Procmonrest from 'procmonrest' // or const Procmonrest = require('procmonrest')

describe('an end-to-end test', function () {
  const serverProcess = new Procmonrest({
      command: 'node .',
      waitFor: /listening on port \d{4,5}/i
    })

  before(() => {
    return serverProcess.start()
  })

  after(() => {
    if (serverProcess.isRunning) {
      return serverProcess.stop()
    }
  })

  ...
})

Be careful!

You can create as many separate instances of Procmonrest as you like; however, keep in mind that you will not be able to run multiple copies of the same child process if they are all competing for the same system resources. For example, you will not be able to run more than one HTTP server locally if they all attempt to listen on the same TCP port.

Therefore, you should carefully plan where in the test suite you will call start() and stop() in order to avoid resource contention.

Documentation

Instances of Procmonrest must be created using the new keyword.

Constructor options

Key	Type	Value
command	{String?}	The command to run (typically, whatever is used to start the local server). Defaults to npm start.
envars	{Object?}	If specified, then these key-value pairs will be added as environment variables for the child process. Defaults to { NODE_ENV: 'test' }.
reference	{String?}	If specified, then this value will be noted inside the log file.
saveLogTo	{String?}	If specified, then the stdout and stderr output of the child process will be saved to this location (instead of the default), which must be an absolute path spec including the file name. Use null or false to prevent the creation of a log file altogether.
waitFor	{RegExp}	A regular expression that each line of output from the child process will be tested against. As soon as a match is made, then the process will be considered "ready for testing".

Properties

isRunning {Boolean}

Returns true when the child process has started and is ready to be tested.

Methods

start returns {Promise}

This spawns the child process, and resolves once the specified pattern is matched in the child process's stdout. The promise will be rejected for any of the following reasons:

1. The process exits before the pattern is matched. If this is the case, then the returned Error object will have a property called exitCode that equals the exit code of the child process.
2. The log file cannot be written to.

stop returns {Promise}

This method calls tree-kill on the child process, and resolves once that is complete. The promise will be rejected if the child process is not running.

Logging

Each instance of Procmonrest saves all stdout and stderr output from the child process to a log file, along with some information about the process itself. The location of the log file defaults to the same as the file containing the code that creates the instance of Procmonrest, and the name will be the same as that file, but with the .js extension changed to .log. For example, if the file containing the code new Procmonrest() is located at test/logging.spec.js, then the log file will be created at test/logging.spec.log.

Each run will create a new log file, and previous versions will be overwritten.

Safety features

In an attempt to avoid any misuse (whether intentional or not), the current working directory for the child process will be the same as the parent.

License

Please refer to LICENSE.