# Node.js Core Test Common Modules

This directory contains modules used to test the Node.js implementation.

## Table of Contents

* [ArrayStream module](#arraystream-module)
* [Benchmark module](#benchmark-module)
* [Common module API](#common-module-api)
* [Countdown module](#countdown-module)
* [CPU Profiler module](#cpu-profiler-module)
* [Debugger module](#debugger-module)
* [DNS module](#dns-module)
* [Duplex pair helper](#duplex-pair-helper)
* [Environment variables](#environment-variables)
* [Fixtures module](#fixtures-module)
* [Heap dump checker module](#heap-dump-checker-module)
* [hijackstdio module](#hijackstdio-module)
* [HTTP2 module](#http2-module)
* [Internet module](#internet-module)
* [ongc module](#ongc-module)
* [Report module](#report-module)
* [tick module](#tick-module)
* [tmpdir module](#tmpdir-module)
* [UDP pair helper](#udp-pair-helper)
* [WPT module](#wpt-module)

## Benchmark Module

The `benchmark` module is used by tests to run benchmarks.

### `runBenchmark(name, env)`

* `name` [\<string>][<string>] Name of benchmark suite to be run.
* `env` [\<Object>][<Object>] Environment variables to be applied during the
  run.

## Common Module API

The `common` module is used by tests for consistency across repeated
tasks.

### `allowGlobals(...allowlist)`

* `allowlist` [\<Array>][<Array>] Array of Globals
* return [\<Array>][<Array>]

Takes `allowlist` and concats that with predefined `knownGlobals`.

### `canCreateSymLink()`

* return [\<boolean>][<boolean>]

Checks whether the current running process can create symlinks. On Windows, this
returns `false` if the process running doesn't have privileges to create
symlinks
([SeCreateSymbolicLinkPrivilege](https://msdn.microsoft.com/en-us/library/windows/desktop/bb530716\(v=vs.85\).aspx)).
On non-Windows platforms, this always returns `true`.

### `createZeroFilledFile(filename)`

Creates a 10 MB file of all null characters.

### `enoughTestMem`

* [\<boolean>][<boolean>]

Indicates if there is more than 1gb of total memory.

### `expectsError(validator[, exact])`

* `validator` [\<Object>][<Object>] | [\<RegExp>][<RegExp>] |
  [\<Function>][<Function>] | [\<Error>][<Error>] The validator behaves
  identical to `assert.throws(fn, validator)`.
* `exact` [\<number>][<number>] default = 1
* return [\<Function>][<Function>] A callback function that expects an error.

A function suitable as callback to validate callback based errors. The error is
validated using `assert.throws(() => { throw error; }, validator)`. If the
returned function has not been called exactly `exact` number of times when the
test is complete, then the test will fail.

### `expectWarning(name[, expected[, code]])`

* `name` [\<string>][<string>] | [\<Object>][<Object>]
* `expected` [\<string>][<string>] | [\<Array>][<Array>] | [\<Object>][<Object>]
* `code` [\<string>][<string>]

Tests whether `name`, `expected`, and `code` are part of a raised warning.

The code is required in case the name is set to `'DeprecationWarning'`.

Examples:

```js
const { expectWarning } = require('../common');

expectWarning('Warning', 'Foobar is really bad');

expectWarning('DeprecationWarning', 'Foobar is deprecated', 'DEP0XXX');

expectWarning('DeprecationWarning', [
  'Foobar is deprecated', 'DEP0XXX',
]);

expectWarning('DeprecationWarning', [
  ['Foobar is deprecated', 'DEP0XXX'],
  ['Baz is also deprecated', 'DEP0XX2'],
]);

expectWarning('DeprecationWarning', {
  DEP0XXX: 'Foobar is deprecated',
  DEP0XX2: 'Baz is also deprecated'
});

expectWarning({
  DeprecationWarning: {
    DEP0XXX: 'Foobar is deprecated',
    DEP0XX1: 'Baz is also deprecated'
  },
  Warning: [
    ['Multiple array entries are fine', 'SpecialWarningCode'],
    ['No code is also fine'],
  ],
  SingleEntry: ['This will also work', 'WarningCode'],
  SingleString: 'Single string entries without code will also work'
});
```

### `getArrayBufferViews(buf)`

* `buf` [\<Buffer>][<Buffer>]
* return [\<ArrayBufferView>][<ArrayBufferView>]\[]

Returns an instance of all possible `ArrayBufferView`s of the provided Buffer.

### `getBufferSources(buf)`

* `buf` [\<Buffer>][<Buffer>]
* return [\<BufferSource>][<BufferSource>]\[]

Returns an instance of all possible `BufferSource`s of the provided Buffer,
consisting of all `ArrayBufferView` and an `ArrayBuffer`.

### `getCallSite(func)`

* `func` [\<Function>][<Function>]
* return [\<string>][<string>]

Returns the file name and line number for the provided Function.

### `getTTYfd()`

Attempts to get a valid TTY file descriptor. Returns `-1` if it fails.

The TTY file descriptor is assumed to be capable of being writable.

### `hasCrypto`

* [\<boolean>][<boolean>]

Indicates whether OpenSSL is available.

### `hasFipsCrypto`

* [\<boolean>][<boolean>]

Indicates that Node.js has been linked with a FIPS compatible OpenSSL library,
and that FIPS as been enabled using `--enable-fips`.

To only detect if the OpenSSL library is FIPS compatible, regardless if it has
been enabled or not, then `process.config.variables.openssl_is_fips` can be
used to determine that situation.

### `hasIntl`

* [\<boolean>][<boolean>]

Indicates if [internationalization][] is supported.

### `hasIPv6`

* [\<boolean>][<boolean>]

Indicates whether `IPv6` is supported on this platform.

### `hasMultiLocalhost`

* [\<boolean>][<boolean>]

Indicates if there are multiple localhosts available.

### `inFreeBSDJail`

* [\<boolean>][<boolean>]

Checks whether free BSD Jail is true or false.

### `isAIX`

* [\<boolean>][<boolean>]

Platform check for Advanced Interactive eXecutive (AIX).

### `isAlive(pid)`

* `pid` [\<number>][<number>]
* return [\<boolean>][<boolean>]

Attempts to 'kill' `pid`

### `isDumbTerminal`

* [\<boolean>][<boolean>]

### `isFreeBSD`

* [\<boolean>][<boolean>]

Platform check for Free BSD.

### `isIBMi`

* [\<boolean>][<boolean>]

Platform check for IBMi.

### `isLinux`

* [\<boolean>][<boolean>]

Platform check for Linux.

### `isLinuxPPCBE`

* [\<boolean>][<boolean>]

Platform check for Linux on PowerPC.

### `isOSX`

* [\<boolean>][<boolean>]

Platform check for macOS.

### `isSunOS`

* [\<boolean>][<boolean>]

Platform check for SunOS.

### `isWindows`

* [\<boolean>][<boolean>]

Platform check for Windows.

### `localhostIPv4`

* [\<string>][<string>]

IP of `localhost`.

### `localIPv6Hosts`

* [\<Array>][<Array>]

Array of IPV6 representations for `localhost`.

### `mustCall([fn][, exact])`

* `fn` [\<Function>][<Function>] default = () => {}
* `exact` [\<number>][<number>] default = 1
* return [\<Function>][<Function>]

Returns a function that calls `fn`. If the returned function has not been called
exactly `exact` number of times when the test is complete, then the test will
fail.

If `fn` is not provided, an empty function will be used.

### `mustCallAtLeast([fn][, minimum])`

* `fn` [\<Function>][<Function>] default = () => {}
* `minimum` [\<number>][<number>] default = 1
* return [\<Function>][<Function>]

Returns a function that calls `fn`. If the returned function has not been called
at least `minimum` number of times when the test is complete, then the test will
fail.

If `fn` is not provided, an empty function will be used.

### `mustNotCall([msg])`

* `msg` [\<string>][<string>] default = 'function should not have been called'
* return [\<Function>][<Function>]

Returns a function that triggers an `AssertionError` if it is invoked. `msg` is
used as the error message for the `AssertionError`.

### `mustSucceed([fn])`

* `fn` [\<Function>][<Function>] default = () => {}
* return [\<Function>][<Function>]

Returns a function that accepts arguments `(err, ...args)`. If `err` is not
`undefined` or `null`, it triggers an `AssertionError`. Otherwise, it calls
`fn(...args)`.

### `nodeProcessAborted(exitCode, signal)`

* `exitCode` [\<number>][<number>]
* `signal` [\<string>][<string>]
* return [\<boolean>][<boolean>]

Returns `true` if the exit code `exitCode` and/or signal name `signal` represent
the exit code and/or signal name of a node process that aborted, `false`
otherwise.

### `opensslCli`

* [\<boolean>][<boolean>]

Indicates whether 'opensslCli' is supported.

### `platformTimeout(ms)`

* `ms` [\<number>][<number>] | [\<bigint>][<bigint>]
* return [\<number>][<number>] | [\<bigint>][<bigint>]

Returns a timeout value based on detected conditions. For example, a debug build
may need extra time so the returned value will be larger than on a release
build.

### `PIPE`

* [\<string>][<string>]

Path to the test socket.

### `PORT`

* [\<number>][<number>]

A port number for tests to use if one is needed.

### `printSkipMessage(msg)`

* `msg` [\<string>][<string>]

Logs '1..0 # Skipped: ' + `msg`

### `pwdCommand`

* [\<array>][<array>] First two argument for the `spawn`/`exec` functions.

Platform normalized `pwd` command options. Usage example:

```js
const common = require('../common');
const { spawn } = require('child_process');

spawn(...common.pwdCommand, { stdio: ['pipe'] });
```

### `requireNoPackageJSONAbove([dir])`

* `dir` [\<string>][<string>] default = \_\_dirname

Throws an `AssertionError` if a `package.json` file exists in any ancestor
directory above `dir`. Such files may interfere with proper test functionality.

### `runWithInvalidFD(func)`

* `func` [\<Function>][<Function>]

Runs `func` with an invalid file descriptor that is an unsigned integer and
can be used to trigger `EBADF` as the first argument. If no such file
descriptor could be generated, a skip message will be printed and the `func`
will not be run.

### `skip(msg)`

* `msg` [\<string>][<string>]

Logs '1..0 # Skipped: ' + `msg` and exits with exit code `0`.

### `skipIfDumbTerminal()`

Skip the rest of the tests if the current terminal is a dumb terminal

### `skipIfEslintMissing()`

Skip the rest of the tests in the current file when `ESLint` is not available
at `tools/node_modules/eslint`

### `skipIfInspectorDisabled()`

Skip the rest of the tests in the current file when the Inspector
was disabled at compile time.

### `skipIf32Bits()`

Skip the rest of the tests in the current file when the Node.js executable
was compiled with a pointer size smaller than 64 bits.

### `skipIfWorker()`

Skip the rest of the tests in the current file when not running on a main
thread.

## ArrayStream Module

The `ArrayStream` module provides a simple `Stream` that pushes elements from
a given array.

<!-- eslint-disable no-undef, node-core/require-common-first, node-core/required-modules -->

```js
const ArrayStream = require('../common/arraystream');
const stream = new ArrayStream();
stream.run(['a', 'b', 'c']);
```

It can be used within tests as a simple mock stream.

## Countdown Module

The `Countdown` module provides a simple countdown mechanism for tests that
require a particular action to be taken after a given number of completed
tasks (for instance, shutting down an HTTP server after a specific number of
requests). The Countdown will fail the test if the remainder did not reach 0.

<!-- eslint-disable strict, node-core/require-common-first, node-core/required-modules -->

```js
const Countdown = require('../common/countdown');

function doSomething() {
  console.log('.');
}

const countdown = new Countdown(2, doSomething);
countdown.dec();
countdown.dec();
```

### `new Countdown(limit, callback)`

* `limit` {number}
* `callback` {function}

Creates a new `Countdown` instance.

### `Countdown.prototype.dec()`

Decrements the `Countdown` counter.

### `Countdown.prototype.remaining`

Specifies the remaining number of times `Countdown.prototype.dec()` must be
called before the callback is invoked.

## CPU Profiler module

The `cpu-prof` module provides utilities related to CPU profiling tests.

### `env`

* Default: { ...process.env, NODE\_DEBUG\_NATIVE: 'INSPECTOR\_PROFILER' }

Environment variables used in profiled processes.

### `getCpuProfiles(dir)`

* `dir` {string} The directory containing the CPU profile files.
* return [\<string>][<string>]

Returns an array of all `.cpuprofile` files found in `dir`.

### `getFrames(file, suffix)`

* `file` {string} Path to a `.cpuprofile` file.
* `suffix` {string} Suffix of the URL of call frames to retrieve.
* returns { frames: [\<Object>][<Object>], nodes: [\<Object>][<Object>] }

Returns an object containing an array of the relevant call frames and an array
of all the profile nodes.

### `kCpuProfInterval`

Sampling interval in microseconds.

### `verifyFrames(output, file, suffix)`

* `output` {string}
* `file` {string}
* `suffix` {string}

Throws an `AssertionError` if there are no call frames with the expected
`suffix` in the profiling data contained in `file`.

## Debugger module

Provides common functionality for tests for `node inspect`.

### `startCLI(args[[, flags], spawnOpts])`

* `args` [\<string>][<string>]
* `flags` [\<string>][<string>] default = \[]
* `showOpts` [\<Object>][<Object>] default = {}
* return [\<Object>][<Object>]

Returns a null-prototype object with properties that are functions and getters
used to interact with the `node inspect` CLI. These functions are:

* `flushOutput()`
* `waitFor()`
* `waitForPrompt()`
* `waitForInitialBreak()`
* `breakInfo`
* `ctrlC()`
* `output`
* `rawOutput`
* `parseSourceLines()`
* `writeLine()`
* `command()`
* `stepCommand()`
* `quit()`

## `DNS` Module

The `DNS` module provides utilities related to the `dns` built-in module.

### `errorLookupMock(code, syscall)`

* `code` [\<string>][<string>] Defaults to `dns.mockedErrorCode`.
* `syscall` [\<string>][<string>] Defaults to `dns.mockedSysCall`.
* return [\<Function>][<Function>]

A mock for the `lookup` option of `net.connect()` that would result in an error
with the `code` and the `syscall` specified. Returns a function that has the
same signature as `dns.lookup()`.

### `mockedErrorCode`

The default `code` of errors generated by `errorLookupMock`.

### `mockedSysCall`

The default `syscall` of errors generated by `errorLookupMock`.

### `readDomainFromPacket(buffer, offset)`

* `buffer` [\<Buffer>][<Buffer>]
* `offset` [\<number>][<number>]
* return [\<Object>][<Object>]

Reads the domain string from a packet and returns an object containing the
number of bytes read and the domain.

### `parseDNSPacket(buffer)`

* `buffer` [\<Buffer>][<Buffer>]
* return [\<Object>][<Object>]

Parses a DNS packet. Returns an object with the values of the various flags of
the packet depending on the type of packet.

### `writeIPv6(ip)`

* `ip` [\<string>][<string>]
* return [\<Buffer>][<Buffer>]

Reads an IPv6 String and returns a Buffer containing the parts.

### `writeDomainName(domain)`

* `domain` [\<string>][<string>]
* return [\<Buffer>][<Buffer>]

Reads a Domain String and returns a Buffer containing the domain.

### `writeDNSPacket(parsed)`

* `parsed` [\<Object>][<Object>]
* return [\<Buffer>][<Buffer>]

Takes in a parsed Object and writes its fields to a DNS packet as a Buffer
object.

## Duplex pair helper

The `common/duplexpair` module exports a single function `makeDuplexPair`,
which returns an object `{ clientSide, serverSide }` where each side is a
`Duplex` stream connected to the other side.

There is no difference between client or server side beyond their names.

## Environment variables

The behavior of the Node.js test suite can be altered using the following
environment variables.

### `NODE_COMMON_PORT`

If set, `NODE_COMMON_PORT`'s value overrides the `common.PORT` default value of
12346\.

### `NODE_SKIP_FLAG_CHECK`

If set, command line arguments passed to individual tests are not validated.

### `NODE_SKIP_CRYPTO`

If set, crypto tests are skipped.

### `NODE_TEST_KNOWN_GLOBALS`

A comma-separated list of variables names that are appended to the global
variable allowlist. Alternatively, if `NODE_TEST_KNOWN_GLOBALS` is set to `'0'`,
global leak detection is disabled.

## Fixtures Module

The `common/fixtures` module provides convenience methods for working with
files in the `test/fixtures` directory.

### `fixtures.fixturesDir`

* [\<string>][<string>]

The absolute path to the `test/fixtures/` directory.

### `fixtures.path(...args)`

* `...args` [\<string>][<string>]

Returns the result of `path.join(fixtures.fixturesDir, ...args)`.

### `fixtures.readSync(args[, enc])`

* `args` [\<string>][<string>] | [\<Array>][<Array>]

Returns the result of
`fs.readFileSync(path.join(fixtures.fixturesDir, ...args), 'enc')`.

### `fixtures.readKey(arg[, enc])`

* `arg` [\<string>][<string>]

Returns the result of
`fs.readFileSync(path.join(fixtures.fixturesDir, 'keys', arg), 'enc')`.

## Heap dump checker module

This provides utilities for checking the validity of heap dumps.
This requires the usage of `--expose-internals`.

### `heap.recordState()`

Create a heap dump and an embedder graph copy for inspection.
The returned object has a `validateSnapshotNodes` function similar to the
one listed below. (`heap.validateSnapshotNodes(...)` is a shortcut for
`heap.recordState().validateSnapshotNodes(...)`.)

### `heap.validateSnapshotNodes(name, expected, options)`

* `name` [\<string>][<string>] Look for this string as the name of heap dump
  nodes.
* `expected` [\<Array>][<Array>] A list of objects, possibly with an `children`
  property that points to expected other adjacent nodes.
* `options` [\<Array>][<Array>]
  * `loose` [\<boolean>][<boolean>] Do not expect an exact listing of
    occurrences of nodes with name `name` in `expected`.

Create a heap dump and an embedder graph copy and validate occurrences.

<!-- eslint-disable no-undef, node-core/require-common-first, node-core/required-modules -->

```js
validateSnapshotNodes('TLSWRAP', [
  {
    children: [
      { name: 'enc_out' },
      { name: 'enc_in' },
      { name: 'TLSWrap' },
    ]
  },
]);
```

## hijackstdio Module

The `hijackstdio` module provides utility functions for temporarily redirecting
`stdout` and `stderr` output.

<!-- eslint-disable no-undef, node-core/require-common-first, node-core/required-modules -->

```js
const { hijackStdout, restoreStdout } = require('../common/hijackstdio');

hijackStdout((data) => {
  /* Do something with data */
  restoreStdout();
});

console.log('this is sent to the hijacked listener');
```

### `hijackStderr(listener)`

* `listener` [\<Function>][<Function>]: a listener with a single parameter
  called `data`.

Eavesdrop to `process.stderr.write()` calls. Once `process.stderr.write()` is
called, `listener` will also be called and the `data` of `write` function will
be passed to `listener`. What's more, `process.stderr.writeTimes` is a count of
the number of calls.

### `hijackStdout(listener)`

* `listener` [\<Function>][<Function>]: a listener with a single parameter
  called `data`.

Eavesdrop to `process.stdout.write()` calls. Once `process.stdout.write()` is
called, `listener` will also be called and the `data` of `write` function will
be passed to `listener`. What's more, `process.stdout.writeTimes` is a count of
the number of calls.

### restoreStderr()

Restore the original `process.stderr.write()`. Used to restore `stderr` to its
original state after calling [`hijackstdio.hijackStdErr()`][].

### restoreStdout()

Restore the original `process.stdout.write()`. Used to restore `stdout` to its
original state after calling [`hijackstdio.hijackStdOut()`][].

## HTTP/2 Module

The http2.js module provides a handful of utilities for creating mock HTTP/2
frames for testing of HTTP/2 endpoints

<!-- eslint-disable no-unused-vars, node-core/require-common-first, node-core/required-modules -->

```js
const http2 = require('../common/http2');
```

### Class: Frame

The `http2.Frame` is a base class that creates a `Buffer` containing a
serialized HTTP/2 frame header.

<!-- eslint-disable no-undef, node-core/require-common-first, node-core/required-modules -->

```js
// length is a 24-bit unsigned integer
// type is an 8-bit unsigned integer identifying the frame type
// flags is an 8-bit unsigned integer containing the flag bits
// id is the 32-bit stream identifier, if any.
const frame = new http2.Frame(length, type, flags, id);

// Write the frame data to a socket
socket.write(frame.data);
```

The serialized `Buffer` may be retrieved using the `frame.data` property.

### Class: DataFrame extends Frame

The `http2.DataFrame` is a subclass of `http2.Frame` that serializes a `DATA`
frame.

<!-- eslint-disable no-undef, node-core/require-common-first, node-core/required-modules -->

```js
// id is the 32-bit stream identifier
// payload is a Buffer containing the DATA payload
// padlen is an 8-bit integer giving the number of padding bytes to include
// final is a boolean indicating whether the End-of-stream flag should be set,
// defaults to false.
const frame = new http2.DataFrame(id, payload, padlen, final);

socket.write(frame.data);
```

### Class: HeadersFrame

The `http2.HeadersFrame` is a subclass of `http2.Frame` that serializes a
`HEADERS` frame.

<!-- eslint-disable no-undef, node-core/require-common-first, node-core/required-modules -->

```js
// id is the 32-bit stream identifier
// payload is a Buffer containing the HEADERS payload (see either
// http2.kFakeRequestHeaders or http2.kFakeResponseHeaders).
// padlen is an 8-bit integer giving the number of padding bytes to include
// final is a boolean indicating whether the End-of-stream flag should be set,
// defaults to false.
const frame = new http2.HeadersFrame(id, payload, padlen, final);

socket.write(frame.data);
```

### Class: SettingsFrame

The `http2.SettingsFrame` is a subclass of `http2.Frame` that serializes an
empty `SETTINGS` frame.

<!-- eslint-disable no-undef, node-core/require-common-first, node-core/required-modules -->

```js
// ack is a boolean indicating whether or not to set the ACK flag.
const frame = new http2.SettingsFrame(ack);

socket.write(frame.data);
```

### `http2.kFakeRequestHeaders`

Set to a `Buffer` instance that contains a minimal set of serialized HTTP/2
request headers to be used as the payload of a `http2.HeadersFrame`.

<!-- eslint-disable no-undef, node-core/require-common-first, node-core/required-modules -->

```js
const frame = new http2.HeadersFrame(1, http2.kFakeRequestHeaders, 0, true);

socket.write(frame.data);
```

### `http2.kFakeResponseHeaders`

Set to a `Buffer` instance that contains a minimal set of serialized HTTP/2
response headers to be used as the payload a `http2.HeadersFrame`.

<!-- eslint-disable no-undef, node-core/require-common-first, node-core/required-modules -->

```js
const frame = new http2.HeadersFrame(1, http2.kFakeResponseHeaders, 0, true);

socket.write(frame.data);
```

### `http2.kClientMagic`

Set to a `Buffer` containing the preamble bytes an HTTP/2 client must send
upon initial establishment of a connection.

<!-- eslint-disable no-undef, node-core/require-common-first, node-core/required-modules -->

```js
socket.write(http2.kClientMagic);
```

## Internet Module

The `common/internet` module provides utilities for working with
internet-related tests.

### `internet.addresses`

* [\<Object>][<Object>]
  * `INET_HOST` [\<string>][<string>] A generic host that has registered common
    DNS records, supports both IPv4 and IPv6, and provides basic HTTP/HTTPS
    services
  * `INET4_HOST` [\<string>][<string>] A host that provides IPv4 services
  * `INET6_HOST` [\<string>][<string>] A host that provides IPv6 services
  * `INET4_IP` [\<string>][<string>] An accessible IPv4 IP, defaults to the
    Google Public DNS IPv4 address
  * `INET6_IP` [\<string>][<string>] An accessible IPv6 IP, defaults to the
    Google Public DNS IPv6 address
  * `INVALID_HOST` [\<string>][<string>] An invalid host that cannot be resolved
  * `MX_HOST` [\<string>][<string>] A host with MX records registered
  * `SRV_HOST` [\<string>][<string>] A host with SRV records registered
  * `PTR_HOST` [\<string>][<string>] A host with PTR records registered
  * `NAPTR_HOST` [\<string>][<string>] A host with NAPTR records registered
  * `SOA_HOST` [\<string>][<string>] A host with SOA records registered
  * `CNAME_HOST` [\<string>][<string>] A host with CNAME records registered
  * `NS_HOST` [\<string>][<string>] A host with NS records registered
  * `TXT_HOST` [\<string>][<string>] A host with TXT records registered
  * `DNS4_SERVER` [\<string>][<string>] An accessible IPv4 DNS server
  * `DNS6_SERVER` [\<string>][<string>] An accessible IPv6 DNS server

A set of addresses for internet-related tests. All properties are configurable
via `NODE_TEST_*` environment variables. For example, to configure
`internet.addresses.INET_HOST`, set the environment
variable `NODE_TEST_INET_HOST` to a specified host.

## ongc Module

The `ongc` module allows a garbage collection listener to be installed. The
module exports a single `onGC()` function.

```js
require('../common');
const onGC = require('../common/ongc');

onGC({}, { ongc() { console.log('collected'); } });
```

### `onGC(target, listener)`

* `target` [\<Object>][<Object>]
* `listener` [\<Object>][<Object>]
  * `ongc` [\<Function>][<Function>]

Installs a GC listener for the collection of `target`.

This uses `async_hooks` for GC tracking. This means that it enables
`async_hooks` tracking, which may affect the test functionality. It also
means that between a `global.gc()` call and the listener being invoked
a full `setImmediate()` invocation passes.

`listener` is an object to make it easier to use a closure; the target object
should not be in scope when `listener.ongc()` is created.

## Report Module

The `report` module provides helper functions for testing diagnostic reporting
functionality.

### `findReports(pid, dir)`

* `pid` [\<number>][<number>] Process ID to retrieve diagnostic report files
  for.
* `dir` [\<string>][<string>] Directory to search for diagnostic report files.
* return [\<Array>][<Array>]

Returns an array of diagnostic report file names found in `dir`. The files
should have been generated by a process whose PID matches `pid`.

### `validate(filepath)`

* `filepath` [\<string>][<string>] Diagnostic report filepath to validate.

Validates the schema of a diagnostic report file whose path is specified in
`filepath`. If the report fails validation, an exception is thrown.

### `validateContent(report)`

* `report` [\<Object>][<Object>] | [\<string>][<string>] JSON contents of a
  diagnostic report file, the parsed Object thereof, or the result of
  `process.report.getReport()`.

Validates the schema of a diagnostic report whose content is specified in
`report`. If the report fails validation, an exception is thrown.

## tick Module

The `tick` module provides a helper function that can be used to call a callback
after a given number of event loop "ticks".

### `tick(x, cb)`

* `x` [\<number>][<number>] Number of event loop "ticks".
* `cb` [\<Function>][<Function>] A callback function.

## tmpdir Module

The `tmpdir` module supports the use of a temporary directory for testing.

### `path`

* [\<string>][<string>]

The realpath of the testing temporary directory.

### `refresh()`

Deletes and recreates the testing temporary directory.

The first time `refresh()` runs, it adds a listener to process `'exit'` that
cleans the temporary directory. Thus, every file under `tmpdir.path` needs to
be closed before the test completes. A good way to do this is to add a
listener to process `'beforeExit'`. If a file needs to be left open until
Node.js completes, use a child process and call `refresh()` only in the
parent.

It is usually only necessary to call `refresh()` once in a test file.
Avoid calling it more than once in an asynchronous context as one call
might refresh the temporary directory of a different context, causing
the test to fail somewhat mysteriously.

## UDP pair helper

The `common/udppair` module exports a function `makeUDPPair` and a class
`FakeUDPWrap`.

`FakeUDPWrap` emits `'send'` events when data is to be sent on it, and provides
an `emitReceived()` API for actin as if data has been received on it.

`makeUDPPair` returns an object `{ clientSide, serverSide }` where each side
is an `FakeUDPWrap` connected to the other side.

There is no difference between cient or server side beyond their names.

## WPT Module

### `harness`

A legacy port of [Web Platform Tests][] harness.

See the source code for definitions. Please avoid using it in new
code - the current usage of this port in tests is being migrated to
the original WPT harness, see [the WPT tests README][].

### Class: WPTRunner

A driver class for running WPT with the WPT harness in a worker thread.

See [the WPT tests README][] for details.

[<Array>]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array
[<ArrayBufferView>]: https://developer.mozilla.org/en-US/docs/Web/API/ArrayBufferView
[<Buffer>]: https://nodejs.org/api/buffer.html#buffer_class_buffer
[<BufferSource>]: https://developer.mozilla.org/en-US/docs/Web/API/BufferSource
[<Error>]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error
[<Function>]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function
[<Object>]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object
[<RegExp>]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp
[<bigint>]: https://github.com/tc39/proposal-bigint
[<boolean>]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type
[<number>]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type
[<string>]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type
[Web Platform Tests]: https://github.com/web-platform-tests/wpt
[`hijackstdio.hijackStdErr()`]: #hijackstderrlistener
[`hijackstdio.hijackStdOut()`]: #hijackstdoutlistener
[internationalization]: ../../doc/api/intl.md
[the WPT tests README]: ../wpt/README.md
