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A test runner so tiny, you have to squint to see it!

If you put test scripts in test/lib, then teenytest's CLI will run them with zero public-API and zero configuration. That's pretty teeny, by the sound of it!


npm i --save-dev teenytest

Using the CLI

teenytest includes a CLI, which can be run ad hoc with:

$(npm bin)/teenytest

By default, the CLI will assume your tests are in "test/lib/**/*.js" and it will search for a test helper in "test/helper.js". You can specify either or both of these by providing arguments, as well:

$(npm bin)/teenytest "test/lib/**/*.js" --helper "test/helper.js"

As an npm script

We prefer including our script in the scripts section of our package.json:

"scripts": {
  "test": "teenytest test/lib/**/*.test.js --helper test/helper.js"

With that configuration above, you could run all your tests with:

npm test

If you want to run a single test, you can just tack an additional path or glob at the end without looking at how teenytest is configured in the package.json:

npm test path/to/my.test.js

The above will ignore the glob embedded in the npm script and only run path/to/my.test.js.

Writing tests

Test styles

Our tests are just Node.js modules. Rather than specify your tests via a fancy testing API, whatever your test modules sets onto module.exports will determine how teenytest will run the test. Modules can export either a single test function or an object of (potentially nested) test functions.

Read on for examples.

Single function tests

If you export a function, that function will be run as a single test. Note that you'll get better test output if you name the function.

var assert = require('assert')

module.exports = function blueIsRed(){
  assert.equal('blue', 'red')

The above test will fail (since 'blue' doesn't equal 'red') with output like:

TAP version 13
not ok 1 - "blueIsRed" - test #1 in `test/lib/single-function.js`
  AssertionError: 'blue' == 'red'
    at blueIsRed (teenytest/example/simple-node/test/lib/single-function.js:4:10)
    at teenytest/index.js:47:9
    at Module._compile (module.js:434:26)

Exporting an object of test functions

If you export an object, you can include as many tests as you like. You can also implement any or all of the four supported test hooks: beforeEach, afterEach, beforeAll, and afterAll.

A file with two tests and all the hooks implemented could look like:

var assert = require('assert')

module.exports = {
  beforeAll: function() { console.log("I'll run once before both tests") },
  beforeEach: function() { console.log("I'll run twice - once before each test") },

  adds: function() { assert.equal(1 + 1, 2) },
  subtracts: function() { assert.equal(4 - 2, 2) },

  afterEach: function() { console.log("I'll run twice - once after each test") },
  afterAll: function() { console.log("I'll run once after both tests") }

This will output what you might expect (be warned: using console.log in your actual tests will make teenytest's output unparseable by TAP reporters):

TAP version 13
I'll run once before both tests
I'll run twice - once before each test
ok 1 - "adds" - test #1 in `test/lib/exporting-an-object.js`
I'll run twice - once after each test
I'll run twice - once before each test
ok 2 - "subtracts" - test #2 in `test/lib/exporting-an-object.js`
I'll run twice - once after each test
I'll run once after both tests

Nested tests

Nested tests are also supported, in which any object can contain any combination of hooks, test functions, and additional sub-test objects. This makes nested teenytest modules very similar to what's possible with "BDD"-like test libraries (in what are traditionally referred to as "example groups" by RSpec, Jasmine, and Mocha parlance).

A common rationale for writing nested tests is to define one nested set of tests for each public method on a subject, for better symmetry between the test and the subject.

Let's see an example. Given this test in test/lib/dog-test.js:

var assert = require('assert')
var Dog = require('../../lib/dog')

module.exports = {
  beforeEach: function () {
    this.subject = new Dog('Sam')
  bark: {
    once: function () {
      assert.deepEqual(this.subject.bark(1), ['Woof #0'])
    twice: function () {
      assert.deepEqual(this.subject.bark(2), ['Woof #0', 'Woof #1'])
  tag: {
    frontSaysName: function () {
      assert.equal(this.subject.tag('front'), 'Hi, I am Sam')
    backSaysAddress: function () {
      assert.equal(this.subject.tag('back'), 'And here is my address')

You'll get this output upon running $ teenytest test/lib/dog-test.js:

TAP version 13
ok 1 - "bark once" - test #1 in `example/simple-node/test/lib/dog-test.js`
ok 2 - "bark twice" - test #2 in `example/simple-node/test/lib/dog-test.js`
ok 3 - "tag frontSaysName" - test #3 in `example/simple-node/test/lib/dog-test.js`
ok 4 - "tag backSaysAddress" - test #4 in `example/simple-node/test/lib/dog-test.js`


One thing you'll notice right away is that teenytest does not ship with its own assertion library. In teenytest, any test that throws an error will trigger a test failure. To keep things simple, the examples in teenytest use Node's built-in assert module, but keep in mind that it isn't intended for public consumption.

If you like the simplicity of the built-in assert, you might want to use its port core-assert. chai is also a very popular choice.

Writing asynchronous tests

With callbacks

Any test hook or test function can also support asynchronous behavior via a callback function. To indicate that a function is asynchronous, add a callback argument to the test method.

For instance, a synchronous test could:

module.exports = function() {
  require('assert').equal(1+1, 2)

But an asynchronous test could specify a done argument and tell teenytest that the test (or hook) is complete by invoking done().

module.exports = function(done) {
    require('assert').equal(1+1, 2)

A test failure can be triggered by either throwing an uncaught exception (which teenytest will be listening for during each asynchronous step) or by passing an Error as the first argument to done.

With promises

If you would prefer to return a promise to manage asynchronous tests, take a look at the teenytest-promise plugin.

Test Helper & Global Hooks

In addition to defining before & after hooks on a per test file basis, teenytest also supports a global test helper, which it will search for by default in test/helper.js, but can be configured with the helperPath configuration option in the API.

An example helper might look like this:

// make global things common across each test to save on per-test setup
global.assert = require('assert')

module.exports = {
  beforeAll: function(){},
  beforeEach: function(){},
  afterEach: function(){},
  afterAll: function(){}

In this case, the beforeAll/afterAll hooks will run only at the beginning and the end of the entire suite (whereas the same hooks exported from a single test file will run before or after all the tests in that same file). The beforeEach/afterEach hooks, meanwhile will run before and after each test in the entire suite.

Advanced CLI Usage


You can configure teenytest via CLI arguments or as properties of a teenytest object in your package.json. A full example follows:

$(npm bin)/teenytest \
  --helper test/support/helper.js \
  --timeout 3000 \
  --configurator config/teenytest.js \
  --plugin test/support/benchmark-plugin.js \
  --plugin teenytest-promise \\

The above is equivalent to the following package.json entry:

"teenytest": {
  "testLocator": "lib/**/*.test.js",
  "helper": "test/support/helper.js",
  "asyncTimeout": 3000,
  "configurator": "config/teenytest.js",
  "plugins": [

These options are available:

  • testLocator - [Default: "test/lib/**/*.js"] - one or more globs which teenytest should use to search for tests. May be a string or an array of strings
  • name - [Default: []] - one or more global name filters to be applied to all files matched by testLocator
  • helper - [Default: "test/helper.js"] - the location of your global test helper file
  • asyncTimeout - [Default: 5000] - the maximum timeout (in milliseconds) for any given test in your suite
  • configurator - [Default: undefined] - a require-able path which exports a function that with parameters (teenytest, cb). Configurator files may be used to run custom code just before the test runner executes the test suite, register or unregister plugins with functions provided by teenytest.plugins, and must invoke the provided callback
  • plugins - [Default: []] - an array of require-able paths which export either teenytest plugin objects or no-arg functions that return plugin objects

Specifying which test files to run

If you'd like to run tests from specific files, you can do that by passing testLocator as an unnamed option on the command line.

teenytest test/foo-test.js

Multiple path/glob options can be passed for testLocator. The following will run all tests in test/specific-foo-test.js as well as any test file matching the glob pattern test/*-bar-test.js.

teenytest test/single-foo-test.js test/*-bar-test.js

Filtering which tests are run

If you'd like to just run one test from a file, you can do that, too!

Locating by name

If you have a test in test/foo-test.js and it exports an object with functions bar and baz, you could tell teenytest to just run baz with:

teenytest test/foo-test.js#baz

The # character will split the glob on the left from the name on the right.

This can even be used across multiple tests in a wildcard glob, allowing you to slice a CI build based on a particular concern, for instance, you could run all audit log tests across your project's modules so long as they name the test the same thing (e.g. teenytest test/**/*.js#audit) to run all of them at once, without necessarily having to split that concern into its own set of files or directories.

Locating by line number

Suppose you have a test in test/bar-test.js and you want to run the test on line 14 (whether that's the line number where the function is declared, or just some line inside the exported test function). You can run just that test with:

teenytest test/bar-test.js:14

Locating with multiple names or line numbers

Each testLocator option can include one name or line number filter suffix. The same glob may be passed multiple times with different suffixes to locate tests matching more than one filter:

teenytest \
  test/foo-test.js#red \
  test/foo-test.js#blue \
  test/bar-test.js:14 \

The above will run tests named red and blue in the file test/foo-test.js and tests on lines 14 and 28 in the file test/bar-test.js.

Locating with the --name option

The --name option may be used to specify a global name filter that will be applied to every testLocator in addition to any filter suffixes provided. The following two commands would result in identical test runs:

teenytest \
teenytest \

--name may be used multiple times to specify more than one global name filter:

teenytest --name=red --name=blue test/foo.test.js

Setting a timeout

By default, teenytest will allow 5 seconds for tests with asynchronous hooks or test functions to run before failing the test with a timeout error. To change this setting, set the --timeout flag in milliseconds:

teenytest --timeout 10000

The above will set the timeout to 10 seconds.


teenytest's output is TAP13-compliant, so its output can be reported on and aggregated with numerous supported continuous integration & reporting tools.

Coverage with istanbul

If you're looking for code coverage, we recommend using istanbul's CLI. To get started, install istanbul locally:

npm i --save-dev istanbul

Suppose you're currently running your teeny tests with:

$(npm bin)/teenytest "lib/**/*.test.js" --helper "test/unit-helper.js"

You can now generate a coverage report for the same test run with:

$(npm bin)/istanbul cover node_modules/teenytest/bin/teenytest -- "lib/**/*.test.js" --helper "test/unit-helper.js"

Note the use of -- before the arguments intended for teenytest itself, which istanbul will forward along.

You could also set up both as npm scripts so you could run either npm test and npm run test:cover by specifying them in your package.json:

"scripts": {
  "test": "teenytest \"lib/**/*.test.js\" --helper test/unit-helper.js",
  "test:cover": "istanbul cover teenytest -- \"lib/**/*.test.js\" --helper test/unit-helper.js"

Other good stuff

Building teenytest plugins

Most of the runtime behavior in teenytest is implemented as plugins that wrap the functions, tests, and suites defined by the user. You can register your own plugin like this:

  name: 'pending',
  interceptors: {
    test: function (runTest, metadata, cb) {
      runTest(function pendingTest(er, results) {
        if (_.startsWith(metadata.name, 'pending') && results.passing) {
          metadata.triggerFailure(new Error('Pending should not pass!'))

The above plugin will fail any tests whose name starts with "pending" but that actually passed. There are several types of plugins, but all of them follow the same theme of wrapping the users' own defined functions and (often nested) suites.

There are two things to keep in mind when designing a plugin: wrapper scopes and lifecycle events.

Plugin wrapper scopes

There are three scopes of specificity each plugin can attach to: userFunction, test, and suite.

userFunction wrappers

A userFunction could be a hook like beforeAll or afterEach or an actual test function. If your plugin should augment or observe the actual behavior of the functions a user defines in their test listings, then you want to define a userFunction plugin.

For example, a plugin below might be a starting point for adding promise support to teenytest:

module.exports = {
  name: 'teenytest-promise',
  translators: {
    userFunction: function (runUserFunction, metadata, cb) {
      runUserFunction(function (er, result) {
        if (typeof result.value === 'object' &&
            typeof result.value['then'] === 'function') {
            function promiseFulfilled (value) {
              cb(er, value)
            function promiseRejected (reason) {
              cb(reason, null)
        } else {

(The above is also the actual source listing of v1.0.0 of the teenytest-promise module.)

test wrappers

Not to be confused with a test function, a test wrapper scope encompasses a test function plus all its hooks. If your plugin is concerned with each test's results, you probably want a test-scoped wrapper.

An example is teenytest's built-in timeout plugin, which guards against tests that take too long:

var timeoutInMs = 1000
  name: 'teenytest-timeout',
  supervisors: {
    test: function (runTest, metadata, cb) {
      var timedOut = false
      var timer = setTimeout(function outtaTime () {
        timedOut = true
        cb(new Error('Test timed out! (timeout: ' + timeoutInMs + 'ms)'))
      }, timeoutInMs)

      runTest(function timerWrappedCallback (er) {
        if (!timedOut) {
suite wrappers

Finally, plugins can also wrap the execution of entire suites of tests using the suite scope. This scope is most often necessary when your plugin wants to comprehend the overall test suite as a tree, and wants to visit each of the suites as nodes on the tree.

This is certainly the least-used scoping, and is most likely to be needed by plugins that gather test results or report on them.

Plugin lifecycle events

The example above defines its wrapper under interceptors, because it needs to run after results have been initially determined but before the results have been logged to the console. Below are the available events to hook into:


Wrapper functions defined under a plugin's translators property will run first, which should enable the author to augment the behavior of the test itself. For instance, one of the first plugins teenytest runs converts all of the user's functions to a consistent async callback API, regardless of whether the user function was asynchronous or not.


Wrapper functions that desire to short-circuit or affect the failure/passing status of a test are implemented under a plugin's supervisors key. Two examples built into teenytest of this are a plugin that enforces a timeout for each test and another that catches uncaught exceptions (i.e. if the user throws error instead of passing it to the callback function).


Wrapper functions that compute results are defined under the analyzers key of a plugin. Teenytest ships with a built-in results plugin & store that is probably fine for most purposes, but if you want to determine the results of your tests some other way, you would define your own analyzers wrappers.

It's important to note that prior to the analyzers lifecycle event, all callbacks pass any test failure as an initial error argument, but—because the built-in results plugin can ensure recorded results are passed to subsequent plugin wrappers' callbacks—any errors up to this point will be swallowed and replaced with null. If a subsequent plugin wrapper passes an error to its own callback function, it will be interpreted by teenytest as a fatal error, aborting the test run.


Sometimes a plugin that plays a supervisory role actually requires knowledge of a test's results in order to determine if a failure occurred. A classic example of this (and perhaps the only use case) are things like "pending test" features, where tests flagged as works-in-progress or "pending" should fail (because they've been marked by the user as unfinished). As a result, a pending test interceptor might trigger a failure for any pending test that passes (perhaps indicating to the user they need to write a failing test or unflag the test as no longer pending).


Reporter wrappers come after all the other plugins, using the provided results callback to write results. By default, teenytest writes out TAP13 to standard out, but a custom reporter could format results any way it likes.

Invoking teenytest via the API

While it'd be unusual to need it, if you require('teenytest'), its exported function looks like:

teenytest(globOfTestPaths, [options], callback)

The function takes a glob pattern describing where your tests are located and an options object with a few simple settings. If your tests pass, the callback's second argument will be true. If your tests fail, it will be false.

Here's an example test script with every option set and a comment on the defaults:

#!/usr/bin/env node

var teenytest = require('teenytest')

teenytest('test/lib/**/*.js', {
  helperPath: 'test/helper.js', // module that exports test hook functions (default: null)
  output: console.log, // output for writing results
  cwd: process.cwd(), // base path for test globs & helper path,
  asyncTimeout: 5000 // milliseconds to wait before triggering failure of async tests & hooks
}, function(er, passing) {
  process.exit(!er && passing ? 0 : 1)

As you can see, the above script will bail with a non-zero exit code if the tests don't pass or if a fatal error occurs.

While the API is asynchronous, but both synchronous and asynchronous tests are supported.

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