Testing and benchmarking


Requires @compas/cli to be installed


A project setup needs a test runner of course. Compas comes with its own test runner loosely inspired by tape. It comes with a few assertions, async testing, and the possibility of doing nesting test suites. AssertionErrors by using Node.js builtin assert -module are handled as well.

Basic test file

A basic test file looks like the following:

import { test } from "@compas/cli";

test("my test", (t) => {
  t.equal(1, 1);
  t.notEqual("foo", "bar");
  t.deepEqual([1, 2], [1, 2]);

Running tests

There are two ways to run tests. The short way is to use compas test which will run all test files in your project. There is also the option to run a test file directly like node ./file.test.js or compas run ./file.test.js. However, to do this you need to add the following to your test file:

import { mainTestFn } from "@compas/cli";


It works based on mainFn as explained in the cli page.

Setup and teardown per test file

Most test runners have a special global function that runs before or after all tests in a single file. This is often called beforeAll / afterAll. We don't need this in the compas provided test runner as all tests run in the order they are specified.

import { test, mainTestFn } from "@compas/cli";


test("setup and teardown", (t) => {
  let myTestGlobal = undefined;

  // Every callback function can be async
  t.test("setup", async () => {
    myTestGlobal = 10;

  t.test("my test global is there", (t) => {
    t.equal(myTestGlobal, 10);

  // In this example not necessary since myTestGlobal will
  // be out of scope for all other code
  t.test("teardown", (t) => {
    myTestGlobal = undefined;
    t.pass("successful teardown");

Asserting on throws

Asserting on throws is another overlooked part of some test runners. This test runner does not provide any fancy util like t.throws(functionThatThrows), but expects the user to use normal control flow like try / catch.

const throws = async () => {
  throw new Error("Oops!");

const doesNotThrow = () => {};

test("Function that throws", async (t) => {
  try {
    await throws();
    // If the function doesn't throw, no assertion is done, which results in a test failure by the runner.
  } catch (e) {
    // A logger from @compas/stdlib is available
    t.equal(e.message, "Oops!");

test("Function that does not throw", async (t) => {
  t.pass("The function did not throw!");
  // If the function does throw, the test runner catches the error and fails this test with the caught exception.

Test configuration

Test configuration is auto loaded from {root}/test/config.js. An example with the defaults is below:

// Individual test timeout, i.e. the function provided to `test` and `t.test`
export const timeout = 2500;

export async function setup() {
  // Global setup function

export async function teardown() {
  // Global teardown function

Timeout is also configurable for subtests via t.timeout like so:

test("configurable timeout", (t) => {
  t.timeout = 20;

  t.test("race with the timeout", async (t) => {
    try {
      await new Promise((resolve) => {
        // No exception happening here
        setTimeout(() => {
        }, 5);
      t.pass("subtest is faster than the parent timeout of 20 milliseconds");
    } catch (e) {
      t.fail("This should not trigger");


Provided by @compas/cli


This marks a file as a test file and starts the test runner when a file is executed directly as Node.js script. It is based on mainFn as explained in the cli page.

There is only a single way to call this function, always:


This call may exists in all test files and does nothing when tests are executed via compas test.

test(name, callback)

This is the only other directly exposed function of the test runner and is used to register tests, also often called a test suite. The callback t contains the functions and properties described below. The callback may be synchronous or return a promise. Any uncaught exception thrown in the callback, will be caught and results in a failed test.


  • name (string): The test suite name
  • callback (function): The test function

A logger instance provided by @compas/stdlib. See logger for more details.


A setter to configure the timeout of subtests registered via t.test. To configure this value see config

t.test(name, callback)

Subtests can be registered any number of levels deep with t.test(), the name and callback work exactly the same as test.

All subtests are executed in the same order as they are registered and will never run in parallel.


t.ok(value, msg?)

Assert that the value passed in is 'truthy'. In JavaScript this is any value except null, undefined, false, "" and 0.

t.notOk(value, msg?)

Assert that the value passed in is 'falsey'. In JavaScript this corresponds to the following values: null, undefined , false, "" and 0.

t.equal(value, expected, msg?)

Assert that value is strict equal to expected.

Some examples:

t.equal(true, true); // Pass
t.equal("foo", "foo"); // Pass

t.equal("foo", "bar"); // Fail
t.equal({}, {}); // Fail

t.notEqual(value, notExpected, msg?)

Assert that value is not strict equal to expected.


Signal to the test runner that an implicit assertion passed. This is often used when testing control flow, like checking that a catch block is executed.


Signal to the test runner that an implicit assertion failed. This is also often used when testing control flow. For example in the following example where the function willThrow should really throw an error.


const willThrow = () => {
  throw new Error("Really did throw");

test("willThrow really throws", (t) => {
  try {
    t.fail("willThrow did not throw.");
  } catch {
    t.pass("willThrow, did indeed throw an error.");

Since the test runner enforces that each test or t.test should either do an assertion or call t.test, the above is more idiomatically written as:


const willThrow = () => {
  throw new Error("Really did throw");

test("willThrow really throws", (t) => {
  try {
  } catch {
    t.pass("willThrow, did indeed throw an error.");

In this case when the willThrow() function doesn't throw, the test runners throws an error that willThrow really throws didn't execute a single assertion. Because the 'catch' block did not executed and consecutively the t.pass() not called.

t.deepEqual(value, expected, msg?)

Compare value and expected using the Node.js built-in deepStrictEqual.


There are two ways to run tests:

  • compas test runs all tests in files where the name ends with .test.js
  • compas ./path/to/file.test.js runs a single test file, provided that the file calls mainTestFn(import.meta).

Whe running all tests, Compas will automatically utilize worker threads to do some parallel test running. Compas will run cpu core count - 1 workers. Workers will execute a single suite and then request a new test file from the runner. All test suites registered by importing a test file, will run in serial on a single worker. Executing with compas test --serial will disable the workers and run all test suite in a single process.

The --watch feature can also be used, via compas test --watch or compas --watch ./path/to/file.test.js. The test runner will then restart when a JavaScript or json file is changed.


When tests are executed, a config file attempted to be loaded from test/config.js. This file can export the following three items:


A configurable timeout in milliseconds. This is enforced for every callback provided to test or t.test. Defaults to 2.5 seconds.


A function that is called before any test file is imported. Executed both for single file tests and when running all tests via compas test. When workers are used as explained in the cli section, all workers will run this setup function. If the function returns a promise, the runner will wait till the promise is resolved before loading any test file.

Note that when a single test file is executed, the test file and it's imports are already resolved before this setup function will be called.


A global teardown function, behaving the same as the previous mentioned setup function. This is called if available, when all test suites did run, regardless of the test result.


On successful runs, the test runner will only print the number of assertions as follows:

12:30:38.640 info[test]
Total assertions: 15
          Passed: 15
          Failed: 0

When tests fail, we have a few options; an assertion failed or an uncaught exception was caught by the runner. These will be printed as follows, with annotated function calls that triggered these errors:

12:42:39.578 error[test]
Total assertions: 6
          Passed: 1
          Failed: 5
failing assertion suite (1/5)
  // t.fail("Fail message")
  fail: Fail message
  // t.ok(false)
    Expected: (boolean) true
    Actual: (boolean) false
  // t.equal("t.equal()", "expected");
  // The type is printed as well, to make it easier to spot when an object is passed in
    Expected: (string) expected
    Actual: (string) "t.equal()"
  // t.deepEqual({ foo: "bar" }, { bar: "foo" });
    Expected values to be strictly deep-equal:
    + actual - expected

    +   foo: 'bar'
    -   bar: 'foo'
uncaught exception suite (0/0)
  // throw new Error("Plain JavaScript error message");
  uncaughtException (0/0)
    Error - Plain JavaScript error message
        name: 'Error',
        message: 'Plain JavaScript error message',
        stack: [
          'at Object.callback (file:///home/dirk/projects/compas-docs/src/exception.test.js:17:11)',
  // throw new AppError("validation.error", 500, { info: "object" });
  @compas/stdlib AppError (0/0)
    AppError: validation.error - 500
        key: 'validation.error',
        status: 500,
        info: { info: 'object' },
        stack: [
          'at Object.callback (file:///home/dirk/projects/compas-docs/src/exception.test.js:21:11)',
        originalError: undefined
  // import assert from "assert";
  // assert.strictEqual("actual", "expected");
  Node.js AssertionError (0/1)
      Expected values to be strictly equal:
      + actual - expected

      + 'actual'
      - 'expected'

Node.js assertions

As noted above t.deepStrictEqual({}, {}) uses a Node.js built-in for the assertion. All other assertion functions from the assert module can be used. The only difference when using these, is that other assertions in the same test function will not run, unlike the assertions provided by Compas. Other assertion libraries that are able to throw Node.js AssertionErrors should be compatible as well, but are not tested.

Randomize rounds

Another feature of the test runner is to run the tests multiple times, changing the order of file loading. This feature can be enabled by using compas test --randomize-rounds=n where n is any integer, for example 3. This may be useful to discover flaky tests or may enable you to do some 'fuzzing' although not completely made for that.

The tests will run as described above, workers will spawn, global setup functions called and test files loaded. However, when tests pass the known test files, ending in .test.js, will be shuffled and run again. On new workers, with a new global setup and teardown call, etc... If any of the runs fail, only the failed result will be printed. When all rounds are successful, the total number of assertions will be printed. This does not work in combination with --serial.


A test runner isn't complete without a coverage checker. So we utilize c8 for that. By running compas coverage collecting coverage is enabled. Check c8 for configuration options.