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spawn processes conveniently in tape tests and match against stdout/stderr streaming output


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npm install tape-spawn


use this in conjunction with tape, e.g.

var test = require('tape')
var spawn = require('tape-spawn')
test('spawn ls', function (t) {
  var st = spawn(t, 'ls ' + __dirname)


If you set DEBUG=tape-spawn in your ENV when running your tests then the STDERR of the spawned child process will be piped into the STDERR of your terminal.


var spawn = require('tape-spawn')

returns a function, spawn, that can be used to spawn new processes and test their output with tape

processes are spawned with npm-execspawn, meaning local node_modules bins will be matched first before looking in your PATH

var spawnTest = spawn(tapeTest, commandString, [options])

returns spawnTest, which can be used to set up assertions. also spawns a process using commandString. options are optional, and can have the following properties:

  • end (default true) - if false no t.end() assertion will be set up for the test, which means you will have to use spawnTest.end(onEnd) to handle it yourself

in addition, the entire options object will get passed as the second argument to spawn, so you can do e.g. {env: {FOO: 'bar'}} to pass env vars to pass custom spawn options (see the child_process node docs for more info)


sets up a tape assertion that expects a non-zero exit code – with an optional message


sets up a tape assertion that expects exit code to equal 0 – with an optional message

spawnTest.exitCode(code, [message])

code must be a number. sets up a tape assertion that expects exit code to equal code – with an optional message

spawnTest.timeout(time, [message])

waits for time milliseconds and then kills the spawned process and fails the test with the optional message string assert message. if message is a function it will be called after the timeout, and no fail assert will be created


sets up a tape assertion for t.end(). if you pass the optional onDone callback, no t.end() assertion will be created, and your onDone callback will be called when the test is done


kills the spawned process


this property is the internally spawned process stdin stream instance

spawnTest.stdout.match(pattern, [message, failMessage])

matches stdout output (assumes utf8 encoding). if pattern is a RegExp it will set up a tape assertion that uses use pattern.test(output). if pattern is a string it will use t.equals() to match the entire output against message. if pattern is a function it should return true/false and take 1 argument, the full output of the spawn

You can pass the optional message or failMessage to customize the tape assertion messages


takes no args. sets up a tape assertion that expects output to match /^$/ (e.g. to be empty)

spawnTest.stderr.match(pattern, [message, failMessage])

the same as spawnTest.stdout.match but matches stderr instead


the same as spawnTest.stdout.empty but matches stderr instead