- Assertion testing
- Asynchronous context tracking
- Async hooks
- Buffer
- C++ addons
- C/C++ addons with Node-API
- C++ embedder API
- Child processes
- Cluster
- Command-line options
- Console
- Corepack
- Crypto
- Debugger
- Deprecated APIs
- Diagnostics Channel
- DNS
- Domain
- Errors
- Events
- File system
- Globals
- HTTP
- HTTP/2
- HTTPS
- Inspector
- Internationalization
- Modules: CommonJS modules
- Modules: ECMAScript modules
- Modules:
node:module
API - Modules: Packages
- Net
- OS
- Path
- Performance hooks
- Permissions
- Process
- Punycode
- Query strings
- Readline
- REPL
- Report
- Single executable applications
- Stream
- String decoder
- Test runner
- Timers
- TLS/SSL
- Trace events
- TTY
- UDP/datagram
- URL
- Utilities
- V8
- VM
- WASI
- Web Crypto API
- Web Streams API
- Worker threads
- Zlib
Node.js v21.0.0-nightly20230525d2a1f71c3e documentation
- Node.js v21.0.0-nightly20230525d2a1f71c3e
-
►
Table of contents
- Test runner
- Subtests
- Skipping tests
describe
/it
syntaxonly
tests- Filtering tests by name
- Extraneous asynchronous activity
- Watch mode
- Running tests from the command line
- Collecting code coverage
- Mocking
- Test reporters
run([options])
test([name][, options][, fn])
test.skip([name][, options][, fn])
test.todo([name][, options][, fn])
test.only([name][, options][, fn])
describe([name][, options][, fn])
describe.skip([name][, options][, fn])
describe.todo([name][, options][, fn])
describe.only([name][, options][, fn])
it([name][, options][, fn])
it.skip([name][, options][, fn])
it.todo([name][, options][, fn])
it.only([name][, options][, fn])
before([fn][, options])
after([fn][, options])
beforeEach([fn][, options])
afterEach([fn][, options])
- Class:
MockFunctionContext
- Class:
MockTracker
- Class:
TestsStream
- Class:
TestContext
context.before([fn][, options])
context.beforeEach([fn][, options])
context.after([fn][, options])
context.afterEach([fn][, options])
context.diagnostic(message)
context.name
context.runOnly(shouldRunOnlyTests)
context.signal
context.skip([message])
context.todo([message])
context.test([name][, options][, fn])
- Class:
SuiteContext
- Test runner
-
►
Index
- Assertion testing
- Asynchronous context tracking
- Async hooks
- Buffer
- C++ addons
- C/C++ addons with Node-API
- C++ embedder API
- Child processes
- Cluster
- Command-line options
- Console
- Corepack
- Crypto
- Debugger
- Deprecated APIs
- Diagnostics Channel
- DNS
- Domain
- Errors
- Events
- File system
- Globals
- HTTP
- HTTP/2
- HTTPS
- Inspector
- Internationalization
- Modules: CommonJS modules
- Modules: ECMAScript modules
- Modules:
node:module
API - Modules: Packages
- Net
- OS
- Path
- Performance hooks
- Permissions
- Process
- Punycode
- Query strings
- Readline
- REPL
- Report
- Single executable applications
- Stream
- String decoder
- Test runner
- Timers
- TLS/SSL
- Trace events
- TTY
- UDP/datagram
- URL
- Utilities
- V8
- VM
- WASI
- Web Crypto API
- Web Streams API
- Worker threads
- Zlib
- ► Other versions
- ► Options
Table of contents
- Test runner
- Subtests
- Skipping tests
describe
/it
syntaxonly
tests- Filtering tests by name
- Extraneous asynchronous activity
- Watch mode
- Running tests from the command line
- Collecting code coverage
- Mocking
- Test reporters
run([options])
test([name][, options][, fn])
test.skip([name][, options][, fn])
test.todo([name][, options][, fn])
test.only([name][, options][, fn])
describe([name][, options][, fn])
describe.skip([name][, options][, fn])
describe.todo([name][, options][, fn])
describe.only([name][, options][, fn])
it([name][, options][, fn])
it.skip([name][, options][, fn])
it.todo([name][, options][, fn])
it.only([name][, options][, fn])
before([fn][, options])
after([fn][, options])
beforeEach([fn][, options])
afterEach([fn][, options])
- Class:
MockFunctionContext
- Class:
MockTracker
- Class:
TestsStream
- Class:
TestContext
context.before([fn][, options])
context.beforeEach([fn][, options])
context.after([fn][, options])
context.afterEach([fn][, options])
context.diagnostic(message)
context.name
context.runOnly(shouldRunOnlyTests)
context.signal
context.skip([message])
context.todo([message])
context.test([name][, options][, fn])
- Class:
SuiteContext
Test runner#
Source Code: lib/test.js
The node:test
module facilitates the creation of JavaScript tests.
To access it:
import test from 'node:test';
const test = require('node:test');
This module is only available under the node:
scheme. The following will not
work:
import test from 'test';
const test = require('test');
Tests created via the test
module consist of a single function that is
processed in one of three ways:
- A synchronous function that is considered failing if it throws an exception, and is considered passing otherwise.
- A function that returns a
Promise
that is considered failing if thePromise
rejects, and is considered passing if thePromise
resolves. - A function that receives a callback function. If the callback receives any
truthy value as its first argument, the test is considered failing. If a
falsy value is passed as the first argument to the callback, the test is
considered passing. If the test function receives a callback function and
also returns a
Promise
, the test will fail.
The following example illustrates how tests are written using the
test
module.
test('synchronous passing test', (t) => {
// This test passes because it does not throw an exception.
assert.strictEqual(1, 1);
});
test('synchronous failing test', (t) => {
// This test fails because it throws an exception.
assert.strictEqual(1, 2);
});
test('asynchronous passing test', async (t) => {
// This test passes because the Promise returned by the async
// function is not rejected.
assert.strictEqual(1, 1);
});
test('asynchronous failing test', async (t) => {
// This test fails because the Promise returned by the async
// function is rejected.
assert.strictEqual(1, 2);
});
test('failing test using Promises', (t) => {
// Promises can be used directly as well.
return new Promise((resolve, reject) => {
setImmediate(() => {
reject(new Error('this will cause the test to fail'));
});
});
});
test('callback passing test', (t, done) => {
// done() is the callback function. When the setImmediate() runs, it invokes
// done() with no arguments.
setImmediate(done);
});
test('callback failing test', (t, done) => {
// When the setImmediate() runs, done() is invoked with an Error object and
// the test fails.
setImmediate(() => {
done(new Error('callback failure'));
});
});
If any tests fail, the process exit code is set to 1
.
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 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 a shorthand for test()
.
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');
});
Filtering tests by name#
The --test-name-pattern
command-line option can be used to only run tests
whose name matches the provided pattern. Test name patterns are interpreted as
JavaScript regular expressions. The --test-name-pattern
option can be
specified multiple times in order to run nested tests. For each test that is
executed, any corresponding test hooks, such as beforeEach()
, are also
run.
Given the following test file, starting Node.js with the
--test-name-pattern="test [1-3]"
option would cause the test runner to execute
test 1
, test 2
, and test 3
. If test 1
did not match the test name
pattern, then its subtests would not execute, despite matching the pattern. The
same set of tests could also be executed by passing --test-name-pattern
multiple times (e.g. --test-name-pattern="test 1"
,
--test-name-pattern="test 2"
, etc.).
test('test 1', async (t) => {
await t.test('test 2');
await t.test('test 3');
});
test('Test 4', async (t) => {
await t.test('Test 5');
await t.test('test 6');
});
Test name patterns can also be specified using regular expression literals. This
allows regular expression flags to be used. In the previous example, starting
Node.js with --test-name-pattern="/test [4-5]/i"
would match Test 4
and
Test 5
because the pattern is case-insensitive.
Test name patterns do not change the set of files that the test runner executes.
Extraneous asynchronous activity#
Once a test function finishes executing, the results are reported 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 later
to the <TestsStream>.
The second setImmediate()
creates an uncaughtException
event.
uncaughtException
and unhandledRejection
events originating from a completed
test are marked as failed by the test
module and reported as diagnostic
warnings at the top level by the <TestsStream>.
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.
});
Watch mode#
The Node.js test runner supports running in watch mode by passing the --watch
flag:
node --test --watch
In watch mode, the test runner will watch for changes to test files and their dependencies. When a change is detected, the test runner will rerun the tests affected by the change. The test runner will continue to run until the process is terminated.
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 singletest
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.
Each test file is executed as if it was a regular script. That is, if the test
file itself uses node:test
to define tests, all of those tests will be
executed within a single application thread, regardless of the value of the
concurrency
option of test()
.
Collecting code coverage#
When Node.js is started with the --experimental-test-coverage
command-line flag, code coverage is collected and statistics are reported once
all tests have completed. If the NODE_V8_COVERAGE
environment variable is
used to specify a code coverage directory, the generated V8 coverage files are
written to that directory. Node.js core modules and files within
node_modules/
directories are not included in the coverage report. If
coverage is enabled, the coverage report is sent to any test reporters via
the 'test:coverage'
event.
Coverage can be disabled on a series of lines using the following comment syntax:
/* node:coverage disable */
if (anAlwaysFalseCondition) {
// Code in this branch will never be executed, but the lines are ignored for
// coverage purposes. All lines following the 'disable' comment are ignored
// until a corresponding 'enable' comment is encountered.
console.log('this is never executed');
}
/* node:coverage enable */
Coverage can also be disabled for a specified number of lines. After the specified number of lines, coverage will be automatically reenabled. If the number of lines is not explicitly provided, a single line is ignored.
/* node:coverage ignore next */
if (anAlwaysFalseCondition) { console.log('this is never executed'); }
/* node:coverage ignore next 3 */
if (anAlwaysFalseCondition) {
console.log('this is never executed');
}
The test runner's code coverage functionality has the following limitations, which will be addressed in a future Node.js release:
- Source maps are not supported.
- Excluding specific files or directories from the coverage report is not supported.
Mocking#
The node:test
module supports mocking during testing via a top-level mock
object. The following example creates a spy on a function that adds two numbers
together. The spy is then used to assert that the function was called as
expected.
import assert from 'node:assert';
import { mock, test } from 'node:test';
test('spies on a function', () => {
const sum = mock.fn((a, b) => {
return a + b;
});
assert.strictEqual(sum.mock.calls.length, 0);
assert.strictEqual(sum(3, 4), 7);
assert.strictEqual(sum.mock.calls.length, 1);
const call = sum.mock.calls[0];
assert.deepStrictEqual(call.arguments, [3, 4]);
assert.strictEqual(call.result, 7);
assert.strictEqual(call.error, undefined);
// Reset the globally tracked mocks.
mock.reset();
});
'use strict';
const assert = require('node:assert');
const { mock, test } = require('node:test');
test('spies on a function', () => {
const sum = mock.fn((a, b) => {
return a + b;
});
assert.strictEqual(sum.mock.calls.length, 0);
assert.strictEqual(sum(3, 4), 7);
assert.strictEqual(sum.mock.calls.length, 1);
const call = sum.mock.calls[0];
assert.deepStrictEqual(call.arguments, [3, 4]);
assert.strictEqual(call.result, 7);
assert.strictEqual(call.error, undefined);
// Reset the globally tracked mocks.
mock.reset();
});
The same mocking functionality is also exposed on the TestContext
object
of each test. The following example creates a spy on an object method using the
API exposed on the TestContext
. The benefit of mocking via the test context is
that the test runner will automatically restore all mocked functionality once
the test finishes.
test('spies on an object method', (t) => {
const number = {
value: 5,
add(a) {
return this.value + a;
},
};
t.mock.method(number, 'add');
assert.strictEqual(number.add.mock.calls.length, 0);
assert.strictEqual(number.add(3), 8);
assert.strictEqual(number.add.mock.calls.length, 1);
const call = number.add.mock.calls[0];
assert.deepStrictEqual(call.arguments, [3]);
assert.strictEqual(call.result, 8);
assert.strictEqual(call.target, undefined);
assert.strictEqual(call.this, number);
});
Test reporters#
The node:test
module supports passing --test-reporter
flags for the test runner to use a specific reporter.
The following built-reporters are supported:
-
tap
Thetap
reporter outputs the test results in the TAP format. -
spec
Thespec
reporter outputs the test results in a human-readable format. -
dot
Thedot
reporter outputs the test results in a compact format, where each passing test is represented by a.
, and each failing test is represented by aX
.
When stdout
is a TTY, the spec
reporter is used by default.
Otherwise, the tap
reporter is used by default.
The exact output of these reporters is subject to change between versions of Node.js, and should not be relied on programmatically. If programmatic access to the test runner's output is required, use the events emitted by the <TestsStream>.
The reporters are available via the node:test/reporters
module:
import { tap, spec, dot } from 'node:test/reporters';
const { tap, spec, dot } = require('node:test/reporters');
Custom reporters#
--test-reporter
can be used to specify a path to custom reporter.
A custom reporter is a module that exports a value
accepted by stream.compose.
Reporters should transform events emitted by a <TestsStream>
Example of a custom reporter using <stream.Transform>:
import { Transform } from 'node:stream';
const customReporter = new Transform({
writableObjectMode: true,
transform(event, encoding, callback) {
switch (event.type) {
case 'test:start':
callback(null, `test ${event.data.name} started`);
break;
case 'test:pass':
callback(null, `test ${event.data.name} passed`);
break;
case 'test:fail':
callback(null, `test ${event.data.name} failed`);
break;
case 'test:plan':
callback(null, 'test plan');
break;
case 'test:diagnostic':
callback(null, event.data.message);
break;
case 'test:coverage': {
const { totalLineCount } = event.data.summary.totals;
callback(null, `total line count: ${totalLineCount}\n`);
break;
}
}
},
});
export default customReporter;
const { Transform } = require('node:stream');
const customReporter = new Transform({
writableObjectMode: true,
transform(event, encoding, callback) {
switch (event.type) {
case 'test:start':
callback(null, `test ${event.data.name} started`);
break;
case 'test:pass':
callback(null, `test ${event.data.name} passed`);
break;
case 'test:fail':
callback(null, `test ${event.data.name} failed`);
break;
case 'test:plan':
callback(null, 'test plan');
break;
case 'test:diagnostic':
callback(null, event.data.message);
break;
case 'test:coverage': {
const { totalLineCount } = event.data.summary.totals;
callback(null, `total line count: ${totalLineCount}\n`);
break;
}
}
},
});
module.exports = customReporter;
Example of a custom reporter using a generator function:
export default async function * customReporter(source) {
for await (const event of source) {
switch (event.type) {
case 'test:start':
yield `test ${event.data.name} started\n`;
break;
case 'test:pass':
yield `test ${event.data.name} passed\n`;
break;
case 'test:fail':
yield `test ${event.data.name} failed\n`;
break;
case 'test:plan':
yield 'test plan';
break;
case 'test:diagnostic':
yield `${event.data.message}\n`;
break;
case 'test:coverage': {
const { totalLineCount } = event.data.summary.totals;
yield `total line count: ${totalLineCount}\n`;
break;
}
}
}
}
module.exports = async function * customReporter(source) {
for await (const event of source) {
switch (event.type) {
case 'test:start':
yield `test ${event.data.name} started\n`;
break;
case 'test:pass':
yield `test ${event.data.name} passed\n`;
break;
case 'test:fail':
yield `test ${event.data.name} failed\n`;
break;
case 'test:plan':
yield 'test plan\n';
break;
case 'test:diagnostic':
yield `${event.data.message}\n`;
break;
case 'test:coverage': {
const { totalLineCount } = event.data.summary.totals;
yield `total line count: ${totalLineCount}\n`;
break;
}
}
}
};
The value provided to --test-reporter
should be a string like one used in an
import()
in JavaScript code, or a value provided for --import
.
Multiple reporters#
The --test-reporter
flag can be specified multiple times to report test
results in several formats. In this situation
it is required to specify a destination for each reporter
using --test-reporter-destination
.
Destination can be stdout
, stderr
, or a file path.
Reporters and destinations are paired according
to the order they were specified.
In the following example, the spec
reporter will output to stdout
,
and the dot
reporter will output to file.txt
:
node --test-reporter=spec --test-reporter=dot --test-reporter-destination=stdout --test-reporter-destination=file.txt
When a single reporter is specified, the destination will default to stdout
,
unless a destination is explicitly provided.
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 test processes would run in parallel, where each process corresponds to one test file. Iftrue
, it would runos.availableParallelism() - 1
test files in parallel. Iffalse
, it would only run one test file at a time. Default:false
.files
: <Array> An array containing the list of files to run. Default matching files from test runner execution model.setup
<Function> A function that accepts theTestsStream
instance and can be used to setup listeners before any tests are run. Default:undefined
.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
.inspectPort
<number> | <Function> Sets inspector port of test child process. This can be a number, or a function that takes no arguments and returns a number. If a nullish value is provided, each process gets its own port, incremented from the primary'sprocess.debugPort
. Default:undefined
.testNamePatterns
<string> | <RegExp> | <Array> A String, RegExp or a RegExp Array, that can be used to only run tests whose name matches the provided pattern. Test name patterns are interpreted as JavaScript regular expressions. For each test that is executed, any corresponding test hooks, such asbeforeEach()
, are also run. Default:undefined
.
- Returns: <TestsStream>
import { tap } from 'node:test/reporters';
import process from 'node:process';
run({ files: [path.resolve('./tests/test.js')] })
.compose(tap)
.pipe(process.stdout);
const { tap } = require('node:test/reporters');
run({ files: [path.resolve('./tests/test.js')] })
.compose(tap)
.pipe(process.stdout);
test([name][, options][, fn])
#
name
<string> The name of the test, which is displayed when reporting test results. Default: Thename
property offn
, or'<anonymous>'
iffn
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 within the application thread. Iftrue
, all scheduled asynchronous tests run concurrently within the thread. Iffalse
, only one test runs 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 runonly
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 asTODO
. If a string is provided, that string is displayed in the test results as the reason why the test isTODO
. 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 aTestContext
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, or immediately if the test runs withindescribe()
.
The test()
function is the value imported from the test
module. Each
invocation of this function results in reporting the test to the <TestsStream>.
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 diagnostic information, or creating subtests.
test()
returns a Promise
that resolves once the test completes.
if test()
is called within a describe()
block, it resolve immediately.
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.
test.skip([name][, options][, fn])
#
Shorthand for skipping a test,
same as test([name], { skip: true }[, fn])
.
test.todo([name][, options][, fn])
#
Shorthand for marking a test as TODO
,
same as test([name], { todo: true }[, fn])
.
test.only([name][, options][, fn])
#
Shorthand for marking a test as only
,
same as test([name], { only: true }[, fn])
.
describe([name][, options][, fn])
#
name
<string> The name of the suite, which is displayed when reporting test results. Default: Thename
property offn
, or'<anonymous>'
iffn
does not have a name.options
<Object> Configuration options for the suite. supports the same options astest([name][, options][, fn])
.fn
<Function> | <AsyncFunction> The function under suite declaring all subtests and subsuites. The first argument to this function is aSuiteContext
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.
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])
.
describe.only([name][, options][, fn])
#
Shorthand for marking a suite as only
, same as
describe([name], { only: true }[, fn])
.
it([name][, options][, fn])
#
Shorthand for test()
.
The it()
function is imported from the node:test
module.
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])
.
it.only([name][, options][, fn])
#
Shorthand for marking a test as only
,
same as it([name], { only: 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(() => console.log('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(() => console.log('finished running a test'));
it('is a subtest', () => {
assert.ok('some relevant assertion here');
});
});
Class: MockFunctionContext
#
The MockFunctionContext
class is used to inspect or manipulate the behavior of
mocks created via the MockTracker
APIs.
ctx.calls
#
A getter that returns a copy of the internal array used to track calls to the mock. Each entry in the array is an object with the following properties.
arguments
<Array> An array of the arguments passed to the mock function.error
<any> If the mocked function threw then this property contains the thrown value. Default:undefined
.result
<any> The value returned by the mocked function.stack
<Error> AnError
object whose stack can be used to determine the callsite of the mocked function invocation.target
<Function> | <undefined> If the mocked function is a constructor, this field contains the class being constructed. Otherwise this will beundefined
.this
<any> The mocked function'sthis
value.
ctx.callCount()
#
- Returns: <integer> The number of times that this mock has been invoked.
This function returns the number of times that this mock has been invoked. This
function is more efficient than checking ctx.calls.length
because ctx.calls
is a getter that creates a copy of the internal call tracking array.
ctx.mockImplementation(implementation)
#
implementation
<Function> | <AsyncFunction> The function to be used as the mock's new implementation.
This function is used to change the behavior of an existing mock.
The following example creates a mock function using t.mock.fn()
, calls the
mock function, and then changes the mock implementation to a different function.
test('changes a mock behavior', (t) => {
let cnt = 0;
function addOne() {
cnt++;
return cnt;
}
function addTwo() {
cnt += 2;
return cnt;
}
const fn = t.mock.fn(addOne);
assert.strictEqual(fn(), 1);
fn.mock.mockImplementation(addTwo);
assert.strictEqual(fn(), 3);
assert.strictEqual(fn(), 5);
});
ctx.mockImplementationOnce(implementation[, onCall])
#
implementation
<Function> | <AsyncFunction> The function to be used as the mock's implementation for the invocation number specified byonCall
.onCall
<integer> The invocation number that will useimplementation
. If the specified invocation has already occurred then an exception is thrown. Default: The number of the next invocation.
This function is used to change the behavior of an existing mock for a single
invocation. Once invocation onCall
has occurred, the mock will revert to
whatever behavior it would have used had mockImplementationOnce()
not been
called.
The following example creates a mock function using t.mock.fn()
, calls the
mock function, changes the mock implementation to a different function for the
next invocation, and then resumes its previous behavior.
test('changes a mock behavior once', (t) => {
let cnt = 0;
function addOne() {
cnt++;
return cnt;
}
function addTwo() {
cnt += 2;
return cnt;
}
const fn = t.mock.fn(addOne);
assert.strictEqual(fn(), 1);
fn.mock.mockImplementationOnce(addTwo);
assert.strictEqual(fn(), 3);
assert.strictEqual(fn(), 4);
});
ctx.resetCalls()
#
Resets the call history of the mock function.
ctx.restore()
#
Resets the implementation of the mock function to its original behavior. The mock can still be used after calling this function.
Class: MockTracker
#
The MockTracker
class is used to manage mocking functionality. The test runner
module provides a top level mock
export which is a MockTracker
instance.
Each test also provides its own MockTracker
instance via the test context's
mock
property.
mock.fn([original[, implementation]][, options])
#
original
<Function> | <AsyncFunction> An optional function to create a mock on. Default: A no-op function.implementation
<Function> | <AsyncFunction> An optional function used as the mock implementation fororiginal
. This is useful for creating mocks that exhibit one behavior for a specified number of calls and then restore the behavior oforiginal
. Default: The function specified byoriginal
.options
<Object> Optional configuration options for the mock function. The following properties are supported:times
<integer> The number of times that the mock will use the behavior ofimplementation
. Once the mock function has been calledtimes
times, it will automatically restore the behavior oforiginal
. This value must be an integer greater than zero. Default:Infinity
.
- Returns: <Proxy> The mocked function. The mocked function contains a special
mock
property, which is an instance ofMockFunctionContext
, and can be used for inspecting and changing the behavior of the mocked function.
This function is used to create a mock function.
The following example creates a mock function that increments a counter by one
on each invocation. The times
option is used to modify the mock behavior such
that the first two invocations add two to the counter instead of one.
test('mocks a counting function', (t) => {
let cnt = 0;
function addOne() {
cnt++;
return cnt;
}
function addTwo() {
cnt += 2;
return cnt;
}
const fn = t.mock.fn(addOne, addTwo, { times: 2 });
assert.strictEqual(fn(), 2);
assert.strictEqual(fn(), 4);
assert.strictEqual(fn(), 5);
assert.strictEqual(fn(), 6);
});
mock.getter(object, methodName[, implementation][, options])
#
This function is syntax sugar for MockTracker.method
with options.getter
set to true
.
mock.method(object, methodName[, implementation][, options])
#
object
<Object> The object whose method is being mocked.methodName
<string> | <symbol> The identifier of the method onobject
to mock. Ifobject[methodName]
is not a function, an error is thrown.implementation
<Function> | <AsyncFunction> An optional function used as the mock implementation forobject[methodName]
. Default: The original method specified byobject[methodName]
.options
<Object> Optional configuration options for the mock method. The following properties are supported:getter
<boolean> Iftrue
,object[methodName]
is treated as a getter. This option cannot be used with thesetter
option. Default: false.setter
<boolean> Iftrue
,object[methodName]
is treated as a setter. This option cannot be used with thegetter
option. Default: false.times
<integer> The number of times that the mock will use the behavior ofimplementation
. Once the mocked method has been calledtimes
times, it will automatically restore the original behavior. This value must be an integer greater than zero. Default:Infinity
.
- Returns: <Proxy> The mocked method. The mocked method contains a special
mock
property, which is an instance ofMockFunctionContext
, and can be used for inspecting and changing the behavior of the mocked method.
This function is used to create a mock on an existing object method. The following example demonstrates how a mock is created on an existing object method.
test('spies on an object method', (t) => {
const number = {
value: 5,
subtract(a) {
return this.value - a;
},
};
t.mock.method(number, 'subtract');
assert.strictEqual(number.subtract.mock.calls.length, 0);
assert.strictEqual(number.subtract(3), 2);
assert.strictEqual(number.subtract.mock.calls.length, 1);
const call = number.subtract.mock.calls[0];
assert.deepStrictEqual(call.arguments, [3]);
assert.strictEqual(call.result, 2);
assert.strictEqual(call.error, undefined);
assert.strictEqual(call.target, undefined);
assert.strictEqual(call.this, number);
});
mock.reset()
#
This function restores the default behavior of all mocks that were previously
created by this MockTracker
and disassociates the mocks from the
MockTracker
instance. Once disassociated, the mocks can still be used, but the
MockTracker
instance can no longer be used to reset their behavior or
otherwise interact with them.
After each test completes, this function is called on the test context's
MockTracker
. If the global MockTracker
is used extensively, calling this
function manually is recommended.
mock.restoreAll()
#
This function restores the default behavior of all mocks that were previously
created by this MockTracker
. Unlike mock.reset()
, mock.restoreAll()
does
not disassociate the mocks from the MockTracker
instance.
mock.setter(object, methodName[, implementation][, options])
#
This function is syntax sugar for MockTracker.method
with options.setter
set to true
.
Class: TestsStream
#
- Extends <ReadableStream>
A successful call to run()
method will return a new <TestsStream>
object, streaming a series of events representing the execution of the tests.
TestsStream
will emit events, in the order of the tests definition
Event: 'test:coverage'
#
data
<Object>summary
<Object> An object containing the coverage report.files
<Array> An array of coverage reports for individual files. Each report is an object with the following schema:path
<string> The absolute path of the file.totalLineCount
<number> The total number of lines.totalBranchCount
<number> The total number of branches.totalFunctionCount
<number> The total number of functions.coveredLineCount
<number> The number of covered lines.coveredBranchCount
<number> The number of covered branches.coveredFunctionCount
<number> The number of covered functions.coveredLinePercent
<number> The percentage of lines covered.coveredBranchPercent
<number> The percentage of branches covered.coveredFunctionPercent
<number> The percentage of functions covered.uncoveredLineNumbers
<Array> An array of integers representing line numbers that are uncovered.
totals
<Object> An object containing a summary of coverage for all files.totalLineCount
<number> The total number of lines.totalBranchCount
<number> The total number of branches.totalFunctionCount
<number> The total number of functions.coveredLineCount
<number> The number of covered lines.coveredBranchCount
<number> The number of covered branches.coveredFunctionCount
<number> The number of covered functions.coveredLinePercent
<number> The percentage of lines covered.coveredBranchPercent
<number> The percentage of branches covered.coveredFunctionPercent
<number> The percentage of functions covered.
workingDirectory
<string> The working directory when code coverage began. This is useful for displaying relative path names in case the tests changed the working directory of the Node.js process.
nesting
<number> The nesting level of the test.
Emitted when code coverage is enabled and all tests have completed.
Event: 'test:diagnostic'
#
data
<Object>file
<string> | <undefined> The path of the test file, undefined if test is not ran through a file.message
<string> The diagnostic message.nesting
<number> The nesting level of the test.
Emitted when context.diagnostic
is called.
Event: 'test:fail'
#
data
<Object>details
<Object> Additional execution metadata.file
<string> | <undefined> The path of the test file, undefined if test is not ran through a file.name
<string> The test name.nesting
<number> The nesting level of the test.testNumber
<number> The ordinal number of the test.todo
<string> | <boolean> | <undefined> Present ifcontext.todo
is calledskip
<string> | <boolean> | <undefined> Present ifcontext.skip
is called
Emitted when a test fails.
Event: 'test:pass'
#
data
<Object>details
<Object> Additional execution metadata.duration
<number> The duration of the test in milliseconds.
file
<string> | <undefined> The path of the test file, undefined if test is not ran through a file.name
<string> The test name.nesting
<number> The nesting level of the test.testNumber
<number> The ordinal number of the test.todo
<string> | <boolean> | <undefined> Present ifcontext.todo
is calledskip
<string> | <boolean> | <undefined> Present ifcontext.skip
is called
Emitted when a test passes.
Event: 'test:plan'
#
data
<Object>file
<string> | <undefined> The path of the test file, undefined if test is not ran through a file.nesting
<number> The nesting level of the test.count
<number> The number of subtests that have ran.
Emitted when all subtests have completed for a given test.
Event: 'test:start'
#
data
<Object>file
<string> | <undefined> The path of the test file, undefined if test is not ran through a file.name
<string> The test name.nesting
<number> The nesting level of the test.
Emitted when a test starts.
Event: 'test:stderr'
#
data
<Object>
Emitted when a running test writes to stderr
.
This event is only emitted if --test
flag is passed.
Event: 'test:stdout'
#
data
<Object>
Emitted when a running test writes to stdout
.
This event is only emitted if --test
flag is passed.
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.before([fn][, options])
#
fn
<Function> | <AsyncFunction> The hook function. The first argument to this function is aTestContext
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 subtest of the current test.
context.beforeEach([fn][, options])
#
fn
<Function> | <AsyncFunction> The hook function. The first argument to this function is aTestContext
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.after([fn][, options])
#
fn
<Function> | <AsyncFunction> The hook function. The first argument to this function is aTestContext
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 that runs after the current test finishes.
test('top level test', async (t) => {
t.after((t) => t.diagnostic(`finished running ${t.name}`));
assert.ok('some relevant assertion here');
});
context.afterEach([fn][, options])
#
fn
<Function> | <AsyncFunction> The hook function. The first argument to this function is aTestContext
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 reported.
This function is used to write 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 runonly
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.
This function causes the test's output to indicate the test as skipped. If
message
is provided, it is included in the 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> OptionalTODO
message.
This function adds a TODO
directive to the test's output. If message
is
provided, it is included in the 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: Thename
property offn
, or'<anonymous>'
iffn
does not have a name.options
<Object> Configuration options for the subtest. The following properties are supported:concurrency
<number> | <boolean> | <null> If a number is provided, then that many tests would run in parallel within the application thread. Iftrue
, it would run all subtests in parallel. Iffalse
, it would only run one test at a time. If unspecified, subtests inherit this value from their parent. Default:null
.only
<boolean> If truthy, and the test context is configured to runonly
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 asTODO
. If a string is provided, that string is displayed in the test results as the reason why the test isTODO
. 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 aTestContext
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.