Node.js v18.9.0 documentation

Subtests#

The test context's test() method allows subtests to be created. This method behaves identically to the top level test() function. The following example demonstrates the creation of a top level test with two subtests.

test('top level test', async (t) => {
  await t.test('subtest 1', (t) => {
    assert.strictEqual(1, 1);
  });

  await t.test('subtest 2', (t) => {
    assert.strictEqual(2, 2);
  });
});

In this example, await is used to ensure that both subtests have completed. This is necessary because parent tests do not wait for their subtests to complete. Any subtests that are still outstanding when their parent finishes are cancelled and treated as failures. Any subtest failures cause the parent test to fail.

Skipping tests#

Individual tests can be skipped by passing the skip option to the test, or by calling the test context's skip() method. Both of these options support including a message that is displayed in the TAP output as shown in the following example.

// The skip option is used, but no message is provided.
test('skip option', { skip: true }, (t) => {
  // This code is never executed.
});

// The skip option is used, and a message is provided.
test('skip option with message', { skip: 'this is skipped' }, (t) => {
  // This code is never executed.
});

test('skip() method', (t) => {
  // Make sure to return here as well if the test contains additional logic.
  t.skip();
});

test('skip() method with message', (t) => {
  // Make sure to return here as well if the test contains additional logic.
  t.skip('this is skipped');
});

describe/it syntax#

Running tests can also be done using describe to declare a suite and it to declare a test. A suite is used to organize and group related tests together. it is an alias for test, except there is no test context passed, since nesting is done using suites.

describe('A thing', () => {
  it('should work', () => {
    assert.strictEqual(1, 1);
  });

  it('should be ok', () => {
    assert.strictEqual(2, 2);
  });

  describe('a nested thing', () => {
    it('should work', () => {
      assert.strictEqual(3, 3);
    });
  });
});

describe and it are imported from the node:test module.

import { describe, it } from 'node:test';const { describe, it } = require('node:test');

only tests#

If Node.js is started with the --test-only command-line option, it is possible to skip all top level tests except for a selected subset by passing the only option to the tests that should be run. When a test with the only option set is run, all subtests are also run. The test context's runOnly() method can be used to implement the same behavior at the subtest level.

// Assume Node.js is run with the --test-only command-line option.
// The 'only' option is set, so this test is run.
test('this test is run', { only: true }, async (t) => {
  // Within this test, all subtests are run by default.
  await t.test('running subtest');

  // The test context can be updated to run subtests with the 'only' option.
  t.runOnly(true);
  await t.test('this subtest is now skipped');
  await t.test('this subtest is run', { only: true });

  // Switch the context back to execute all tests.
  t.runOnly(false);
  await t.test('this subtest is now run');

  // Explicitly do not run these tests.
  await t.test('skipped subtest 3', { only: false });
  await t.test('skipped subtest 4', { skip: true });
});

// The 'only' option is not set, so this test is skipped.
test('this test is not run', () => {
  // This code is not run.
  throw new Error('fail');
});

Extraneous asynchronous activity#

Once a test function finishes executing, the TAP results are output as quickly as possible while maintaining the order of the tests. However, it is possible for the test function to generate asynchronous activity that outlives the test itself. The test runner handles this type of activity, but does not delay the reporting of test results in order to accommodate it.

In the following example, a test completes with two setImmediate() operations still outstanding. The first setImmediate() attempts to create a new subtest. Because the parent test has already finished and output its results, the new subtest is immediately marked as failed, and reported in the top level of the file's TAP output.

The second setImmediate() creates an uncaughtException event. uncaughtException and unhandledRejection events originating from a completed test are handled by the test module and reported as diagnostic warnings in the top level of the file's TAP output.

test('a test that creates asynchronous activity', (t) => {
  setImmediate(() => {
    t.test('subtest that is created too late', (t) => {
      throw new Error('error1');
    });
  });

  setImmediate(() => {
    throw new Error('error2');
  });

  // The test finishes after this line.
});

Running tests from the command line#

The Node.js test runner can be invoked from the command line by passing the --test flag:

node --test

By default, Node.js will recursively search the current directory for JavaScript source files matching a specific naming convention. Matching files are executed as test files. More information on the expected test file naming convention and behavior can be found in the test runner execution model section.

Alternatively, one or more paths can be provided as the final argument(s) to the Node.js command, as shown below.

node --test test1.js test2.mjs custom_test_dir/

In this example, the test runner will execute the files test1.js and test2.mjs. The test runner will also recursively search the custom_test_dir/ directory for test files to execute.

Test runner execution model#

When searching for test files to execute, the test runner behaves as follows:

• Any files explicitly provided by the user are executed.
• If the user did not explicitly specify any paths, the current working directory is recursively searched for files as specified in the following steps.
• node_modules directories are skipped unless explicitly provided by the user.
• If a directory named test is encountered, the test runner will search it recursively for all all .js, .cjs, and .mjs files. All of these files are treated as test files, and do not need to match the specific naming convention detailed below. This is to accommodate projects that place all of their tests in a single test directory.
• In all other directories, .js, .cjs, and .mjs files matching the following patterns are treated as test files:
  • ^test$ - Files whose basename is the string 'test'. Examples: test.js, test.cjs, test.mjs.
  • ^test-.+ - Files whose basename starts with the string 'test-' followed by one or more characters. Examples: test-example.js, test-another-example.mjs.
  • .+[\.\-\_]test$ - Files whose basename ends with .test, -test, or _test, preceded by one or more characters. Examples: example.test.js, example-test.cjs, example_test.mjs.
  • Other file types understood by Node.js such as .node and .json are not automatically executed by the test runner, but are supported if explicitly provided on the command line.

Each matching test file is executed in a separate child process. If the child process finishes with an exit code of 0, the test is considered passing. Otherwise, the test is considered to be a failure. Test files must be executable by Node.js, but are not required to use the node:test module internally.

run([options])#

• options <Object> Configuration options for running tests. The following properties are supported:
  • concurrency <number> | <boolean> If a number is provided, then that many files would run in parallel. If truthy, it would run (number of cpu cores - 1) files in parallel. If falsy, it would only run one file at a time. If unspecified, subtests inherit this value from their parent. Default: true.
  • files: <Array> An array containing the list of files to run. Default matching files from test runner execution model.
  • signal <AbortSignal> Allows aborting an in-progress test execution.
  • timeout <number> A number of milliseconds the test execution will fail after. If unspecified, subtests inherit this value from their parent. Default: Infinity.
• Returns: <TapStream>

run({ files: [path.resolve('./tests/test.js')] })
  .pipe(process.stdout);

test([name][, options][, fn])#

• name <string> The name of the test, which is displayed when reporting test results. Default: The name property of fn, or '<anonymous>' if fn does not have a name.
• options <Object> Configuration options for the test. The following properties are supported:
  • concurrency <number> | <boolean> If a number is provided, then that many tests would run in parallel. If truthy, it would run (number of cpu cores - 1) tests in parallel. For subtests, it will be Infinity tests in parallel. If falsy, it would only run one test at a time. If unspecified, subtests inherit this value from their parent. Default: false.
  • only <boolean> If truthy, and the test context is configured to run only tests, then this test will be run. Otherwise, the test is skipped. Default: false.
  • signal <AbortSignal> Allows aborting an in-progress test.
  • skip <boolean> | <string> If truthy, the test is skipped. If a string is provided, that string is displayed in the test results as the reason for skipping the test. Default: false.
  • todo <boolean> | <string> If truthy, the test marked as TODO. If a string is provided, that string is displayed in the test results as the reason why the test is TODO. Default: false.
  • timeout <number> A number of milliseconds the test will fail after. If unspecified, subtests inherit this value from their parent. Default: Infinity.
• fn <Function> | <AsyncFunction> The function under test. The first argument to this function is a TestContext object. If the test uses callbacks, the callback function is passed as the second argument. Default: A no-op function.
• Returns: <Promise> Resolved with undefined once the test completes.

The test() function is the value imported from the test module. Each invocation of this function results in the creation of a test point in the TAP output.

The TestContext object passed to the fn argument can be used to perform actions related to the current test. Examples include skipping the test, adding additional TAP diagnostic information, or creating subtests.

test() returns a Promise that resolves once the test completes. The return value can usually be discarded for top level tests. However, the return value from subtests should be used to prevent the parent test from finishing first and cancelling the subtest as shown in the following example.

test('top level test', async (t) => {
  // The setTimeout() in the following subtest would cause it to outlive its
  // parent test if 'await' is removed on the next line. Once the parent test
  // completes, it will cancel any outstanding subtests.
  await t.test('longer running subtest', async (t) => {
    return new Promise((resolve, reject) => {
      setTimeout(resolve, 1000);
    });
  });
});

The timeout option can be used to fail the test if it takes longer than timeout milliseconds to complete. However, it is not a reliable mechanism for canceling tests because a running test might block the application thread and thus prevent the scheduled cancellation.

describe([name][, options][, fn])#

• name <string> The name of the suite, which is displayed when reporting test results. Default: The name property of fn, or '<anonymous>' if fn does not have a name.
• options <Object> Configuration options for the suite. supports the same options as test([name][, options][, fn]).
• fn <Function> | <AsyncFunction> The function under suite declaring all subtests and subsuites. The first argument to this function is a SuiteContext object. Default: A no-op function.
• Returns: undefined.

The describe() function imported from the node:test module. Each invocation of this function results in the creation of a Subtest and a test point in the TAP output. After invocation of top level describe functions, all top level tests and suites will execute.

describe.skip([name][, options][, fn])#

Shorthand for skipping a suite, same as describe([name], { skip: true }[, fn]).

describe.todo([name][, options][, fn])#

Shorthand for marking a suite as TODO, same as describe([name], { todo: true }[, fn]).

it([name][, options][, fn])#

• name <string> The name of the test, which is displayed when reporting test results. Default: The name property of fn, or '<anonymous>' if fn does not have a name.
• options <Object> Configuration options for the suite. supports the same options as test([name][, options][, fn]).
• fn <Function> | <AsyncFunction> The function under test. If the test uses callbacks, the callback function is passed as an argument. Default: A no-op function.
• Returns: undefined.

The it() function is the value imported from the node:test module. Each invocation of this function results in the creation of a test point in the TAP output.

it.skip([name][, options][, fn])#

Shorthand for skipping a test, same as it([name], { skip: true }[, fn]).

it.todo([name][, options][, fn])#

Shorthand for marking a test as TODO, same as it([name], { todo: true }[, fn]).

before([, fn][, options])#

• fn <Function> | <AsyncFunction> The hook function. If the hook uses callbacks, the callback function is passed as the second argument. Default: A no-op function.
• options <Object> Configuration options for the hook. The following properties are supported:
  • signal <AbortSignal> Allows aborting an in-progress hook.
  • timeout <number> A number of milliseconds the hook will fail after. If unspecified, subtests inherit this value from their parent. Default: Infinity.

This function is used to create a hook running before running a suite.

describe('tests', async () => {
  before(() => console.log('about to run some test'));
  it('is a subtest', () => {
    assert.ok('some relevant assertion here');
  });
});

after([, fn][, options])#

• fn <Function> | <AsyncFunction> The hook function. If the hook uses callbacks, the callback function is passed as the second argument. Default: A no-op function.
• options <Object> Configuration options for the hook. The following properties are supported:
  • signal <AbortSignal> Allows aborting an in-progress hook.
  • timeout <number> A number of milliseconds the hook will fail after. If unspecified, subtests inherit this value from their parent. Default: Infinity.

This function is used to create a hook running after running a suite.

describe('tests', async () => {
  after(() => console.log('finished running tests'));
  it('is a subtest', () => {
    assert.ok('some relevant assertion here');
  });
});

beforeEach([, fn][, options])#

• fn <Function> | <AsyncFunction> The hook function. If the hook uses callbacks, the callback function is passed as the second argument. Default: A no-op function.
• options <Object> Configuration options for the hook. The following properties are supported:
  • signal <AbortSignal> Allows aborting an in-progress hook.
  • timeout <number> A number of milliseconds the hook will fail after. If unspecified, subtests inherit this value from their parent. Default: Infinity.

This function is used to create a hook running before each subtest of the current suite.

describe('tests', async () => {
  beforeEach(() => t.diagnostic('about to run a test'));
  it('is a subtest', () => {
    assert.ok('some relevant assertion here');
  });
});

afterEach([, fn][, options])#

• fn <Function> | <AsyncFunction> The hook function. If the hook uses callbacks, the callback function is passed as the second argument. Default: A no-op function.
• options <Object> Configuration options for the hook. The following properties are supported:
  • signal <AbortSignal> Allows aborting an in-progress hook.
  • timeout <number> A number of milliseconds the hook will fail after. If unspecified, subtests inherit this value from their parent. Default: Infinity.

This function is used to create a hook running after each subtest of the current test.

describe('tests', async () => {
  afterEach(() => t.diagnostic('about to run a test'));
  it('is a subtest', () => {
    assert.ok('some relevant assertion here');
  });
});

Class: TapStream#

• Extends <ReadableStream>

A successful call to run() method will return a new <TapStream> object, streaming a TAP output TapStream will emit events, in the order of the tests definition

Event: 'test:diagnostic'#

• message <string> The diagnostic message.

Emitted when context.diagnostic is called.

Event: 'test:fail'#

• data <Object>
  • duration <number> The test duration.
  • error <Error> The failure casing test to fail.
  • name <string> The test name.
  • testNumber <number> The ordinal number of the test.
  • todo <string> | <undefined> Present if context.todo is called
  • skip <string> | <undefined> Present if context.skip is called

Emitted when a test fails.

Event: 'test:pass'#

• data <Object>
  • duration <number> The test duration.
  • name <string> The test name.
  • testNumber <number> The ordinal number of the test.
  • todo <string> | <undefined> Present if context.todo is called
  • skip <string> | <undefined> Present if context.skip is called

Emitted when a test passes.

Class: TestContext#

An instance of TestContext is passed to each test function in order to interact with the test runner. However, the TestContext constructor is not exposed as part of the API.

context.beforeEach([, fn][, options])#

• fn <Function> | <AsyncFunction> The hook function. The first argument to this function is a TestContext object. If the hook uses callbacks, the callback function is passed as the second argument. Default: A no-op function.
• options <Object> Configuration options for the hook. The following properties are supported:
  • signal <AbortSignal> Allows aborting an in-progress hook.
  • timeout <number> A number of milliseconds the hook will fail after. If unspecified, subtests inherit this value from their parent. Default: Infinity.

This function is used to create a hook running before each subtest of the current test.

test('top level test', async (t) => {
  t.beforeEach((t) => t.diagnostic(`about to run ${t.name}`));
  await t.test(
    'This is a subtest',
    (t) => {
      assert.ok('some relevant assertion here');
    }
  );
});

context.afterEach([, fn][, options])#

• fn <Function> | <AsyncFunction> The hook function. The first argument to this function is a TestContext object. If the hook uses callbacks, the callback function is passed as the second argument. Default: A no-op function.
• options <Object> Configuration options for the hook. The following properties are supported:
  • signal <AbortSignal> Allows aborting an in-progress hook.
  • timeout <number> A number of milliseconds the hook will fail after. If unspecified, subtests inherit this value from their parent. Default: Infinity.

This function is used to create a hook running after each subtest of the current test.

test('top level test', async (t) => {
  t.afterEach((t) => t.diagnostic(`finished running ${t.name}`));
  await t.test(
    'This is a subtest',
    (t) => {
      assert.ok('some relevant assertion here');
    }
  );
});

context.diagnostic(message)#

• message <string> Message to be displayed as a TAP diagnostic.

This function is used to write TAP diagnostics to the output. Any diagnostic information is included at the end of the test's results. This function does not return a value.

test('top level test', (t) => {
  t.diagnostic('A diagnostic message');
});

context.name#

The name of the test.

context.runOnly(shouldRunOnlyTests)#

• shouldRunOnlyTests <boolean> Whether or not to run only tests.

If shouldRunOnlyTests is truthy, the test context will only run tests that have the only option set. Otherwise, all tests are run. If Node.js was not started with the --test-only command-line option, this function is a no-op.

test('top level test', (t) => {
  // The test context can be set to run subtests with the 'only' option.
  t.runOnly(true);
  return Promise.all([
    t.test('this subtest is now skipped'),
    t.test('this subtest is run', { only: true }),
  ]);
});

context.signal#

• <AbortSignal> Can be used to abort test subtasks when the test has been aborted.

test('top level test', async (t) => {
  await fetch('some/uri', { signal: t.signal });
});

context.skip([message])#

• message <string> Optional skip message to be displayed in TAP output.

This function causes the test's output to indicate the test as skipped. If message is provided, it is included in the TAP output. Calling skip() does not terminate execution of the test function. This function does not return a value.

test('top level test', (t) => {
  // Make sure to return here as well if the test contains additional logic.
  t.skip('this is skipped');
});

context.todo([message])#

• message <string> Optional TODO message to be displayed in TAP output.

This function adds a TODO directive to the test's output. If message is provided, it is included in the TAP output. Calling todo() does not terminate execution of the test function. This function does not return a value.

test('top level test', (t) => {
  // This test is marked as `TODO`
  t.todo('this is a todo');
});

context.test([name][, options][, fn])#

• name <string> The name of the subtest, which is displayed when reporting test results. Default: The name property of fn, or '<anonymous>' if fn does not have a name.
• options <Object> Configuration options for the subtest. The following properties are supported:
  • concurrency <number> The number of tests that can be run at the same time. If unspecified, subtests inherit this value from their parent. Default: 1.
  • only <boolean> If truthy, and the test context is configured to run only tests, then this test will be run. Otherwise, the test is skipped. Default: false.
  • signal <AbortSignal> Allows aborting an in-progress test.
  • skip <boolean> | <string> If truthy, the test is skipped. If a string is provided, that string is displayed in the test results as the reason for skipping the test. Default: false.
  • todo <boolean> | <string> If truthy, the test marked as TODO. If a string is provided, that string is displayed in the test results as the reason why the test is TODO. Default: false.
  • timeout <number> A number of milliseconds the test will fail after. If unspecified, subtests inherit this value from their parent. Default: Infinity.
• fn <Function> | <AsyncFunction> The function under test. The first argument to this function is a TestContext object. If the test uses callbacks, the callback function is passed as the second argument. Default: A no-op function.
• Returns: <Promise> Resolved with undefined once the test completes.

This function is used to create subtests under the current test. This function behaves in the same fashion as the top level test() function.

test('top level test', async (t) => {
  await t.test(
    'This is a subtest',
    { only: false, skip: false, concurrency: 1, todo: false },
    (t) => {
      assert.ok('some relevant assertion here');
    }
  );
});

Class: SuiteContext#

An instance of SuiteContext is passed to each suite function in order to interact with the test runner. However, the SuiteContext constructor is not exposed as part of the API.

context.name#

The name of the suite.

context.signal#

• <AbortSignal> Can be used to abort test subtasks when the test has been aborted.