stub-spawn-once

Stubs child_process.spawn for a single command; cleans up afterwards. Perfect for testing.

Why

Mocking child_process.spawn is hard. See for yourself - the stubbing api for your tests is hard in mock-spawn or spawn-mock. I wanted something much simpler: just specify exit code and stdout and stderr for a single execution. This module does this

const execa = require('execa') // or any module
const { stubSpawnOnce } = require('.')
stubSpawnOnce(
  '/bin/sh -c echo "hello"',
  0, // exit code
  'hi from stub!', // stdout
  'and some error output' // stderr
)
execa
  .shell('echo "hello"')
  .then(console.log)
  /*
    output:
    {
      stdout: 'hi from stub!',
      stderr: 'and some error output',
      code: 0,
      failed: false,
      killed: false,
      signal: null,
      cmd: '/bin/sh -c echo "hello"',
      timedOut: false
    }
  */
  .then(() => {
    // call command again - the stub is gone
    return execa.shell('echo "hello"')
  })
  .then(console.log)
  /*
    output:
    {
      stdout: 'hello',
      stderr: '',
      code: 0,
      failed: false,
      killed: false,
      signal: null,
      cmd: '/bin/sh -c echo "hello"',
      timedOut: false
    }
  */

*hint exit code argument is optional and you can omit it (then 0 will be returned)

const { stubSpawnShellOnce } = require('.')
stubSpawnShellOnce('my command', 'hi there', 'error output string')

Install

Requires Node version 6 or above.

npm install --save-dev stub-spawn-once

Use

Examples from Mocha unit tests. Common information

• only the given command is stubbed, other spawn commands are unaffected by the stub.
• a stub will be removed after it runs once.

stubSpawnOnce

const { stubSpawnOnce } = require('stub-spawn-once')
const execa = require('execa')
it('prints mock output', () => {
  const cmd = 'echo "hello"'
  // output "foo" instead of "hello"
  stubSpawnOnce(`/bin/sh -c ${cmd}`, 0, 'foo', 'bar')
  return execa.shell(cmd)
    .then(result => {
      // result.code = 0
      // result.stdout = "foo"
      // result.stderr = "bar"
    })
})

stubSpawnShellOnce

const { stubSpawnShellOnce } = require('stub-spawn-once')
const execa = require('execa')
it('prints mock output', () => {
  const cmd = 'echo "hello"'
  // output "foo" instead of "hello"
  stubSpawnShellOnce(cmd, 0, 'foo', 'bar')
  return execa.shell(cmd)
    .then(result => {
      // result.code = 0
      // result.stdout = "foo"
      // result.stderr = "bar"
    })
})

Bonus

As a bonus, this module also mocks child_process.execFile allowing you easy testing.

const {stubSpawnOnce} = require('stub-spawn-once')
stubSpawnOnce('echo "hello"', 0, 'foo', 'bar')
const cp = require('child_process')
cp.exec('echo "hello"', (code, out, errors) => {
  // code is 0
  // out is "foo"
  // errors is "bar"
})

You can use alias stubExecOnce to stubSpawnOnce

const {stubExecOnce} = require('stub-spawn-once')
stubExecOnce('echo "hi"', "bye")

Small print

Author: Gleb Bahmutov <[email protected]> © 2017

• @bahmutov
• glebbahmutov.com
• blog

License: MIT - do anything with the code, but don't blame me if it does not work.

Support: if you find any problems with this module, email / tweet / open issue on Github

MIT License

Copyright (c) 2017 Gleb Bahmutov <[email protected]>

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.