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Node.js v18.0.0-v8-canary20220401d5709d7181 documentation
- Node.js v18.0.0-v8-canary20220401d5709d7181
- ► Table of contents
-
►
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:
module
API - Modules: Packages
- Net
- OS
- Path
- Performance hooks
- Policies
- Process
- Punycode
- Query strings
- Readline
- REPL
- Report
- 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
- ► Options
Table of contents
Test runner#
Source Code: lib/test.js
The node:test
module facilitates the creation of JavaScript tests that
report results in TAP format. 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'));
});
});
As a test file executes, TAP is written to the standard output of the Node.js
process. This output can be interpreted by any test harness that understands
the TAP format. 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. 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');
});
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.
});
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> The number of tests that can be run at the same time. If unspecified, subtests inherit this value from their parent. Default:1
.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
.
fn
<Function> | <AsyncFunction> The function under test. This 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.
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);
});
});
});
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.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.
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.
context.todo([message])
#
message
<string> OptionalTODO
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.
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> The number of tests that can be run at the same time. If unspecified, subtests inherit this value from their parent. Default:1
.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
.
fn
<Function> | <AsyncFunction> The function under test. This 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.