Folio

A customizable test framework to build your own test frameworks. Foundation for the Playwright test runner.

Folio is available in preview and is under active development. Breaking changes could happen. We welcome your feedback to shape this towards 1.0.

Docs

Isolation and flexibility
Writing a test
Writing a configuration file
Creating an environment
Command line
Snapshots
Annotations
- Flaky tests
Parallelism and sharding
- Workers
- Shards
Advanced configuration
Reporters
- Built-in reporters
- Reporter API
Expect
- Add custom matchers using expect.extend

Isolation and flexibility

Folio focuses on test isolation and flexibility. This makes it fast, reliable and able to adapt to your specific needs.

Isolation. Tests are isolated by default and can be run independently.

Folio runs tests in parallel by default, making your test suite much faster. Thanks to isolation, Folio reuses processes for multiple tests, suites and file, which makes it even faster.
Flaky tests can be retried without significant overhead, because Folio will only retry the failures, and not the whole suite.
Refactoring tests and moving them around is effortless, since isolated tests do not have inter-dependencies.
You can group tests based on their meaning, instead of their common setup.

Flexibility. Folio includes advanced features, adapting to your specific testing needs.

Leverage TypeScript power with minimal effort.
Run tests in multiple configurations.
Annotate tests as skipped/failed based on configuration.
Generate comprehensive report with your custom test annotations.
Define multiple test types, for example slow tests or smoke tests, and run them differently.

Writing a test

Folio follows the traditional BDD style. However, each test in Folio receives an object with Test Arguments. These arguments are isolated from other tests, which gives Folio numerous advantages.

test('insert an entry', async ({ table }) => {
  await table.insert({ username: 'folio', password: 'testing' });
  const entry = await table.query({ username: 'folio' });
  expect(entry.password).toBe('testing');
});

In the test above, table is a database table created for each test, so multiple tests running in parallel won't step on each other's toes.

Folio uses expect library for test assertions.

Writing a configuration file

Folio requires a configuration file that specifies how to run the tests.

// folio.config.ts

import * as folio from 'folio';

// Configure Folio to look for tests in this directory, and give each test 20 seconds.
folio.setConfig({ testDir: __dirname, timeout: 20000 });

// Create a test type. For the easiest setup, you can use a default one.
export const test = folio.test;

// Run tests with two retries.
test.runWith({ tag: 'basic', retries: 2 });

Now, use the created test type in your tests.

// math.spec.ts

import { test } from './folio.config';

test('check the addition', () => {
  test.expect(1 + 1).toBe(42);
});

You can run tests with Folio command line:

$ npx folio --reporter=dot
Running 1 test using 1 worker
××F
 1 failed

Creating an environment

Usually, you need some test environment to run the tests. That may be a test database, dev server, mock user data, or anything else the test needs. Folio support creating an environment that is going to be used for multiple tests.

Let's see how to add an environment, based on the example from writing a configuration file section.

// folio.config.ts

import * as folio from 'folio';

folio.setConfig({ testDir: __dirname, timeout: 20000 });

class DatabaseEnv {
  database: Database;
  table: DatabaseTable;

  async beforeAll() {
    // Connect to a database once, it is expensive.
    this.database = await connectToTestDatabase();
  }

  async beforeEach() {
    // Create a new table for each test and return it.
    this.table = await this.database.createTable();
    // Anything returned from this method is available to the test. In our case, "table".
    return { table: this.table };
  }

  async afterEach() {
    // Do not leave extra tables around.
    await this.table.drop();
  }

  async afterAll() {
    await this.database.disconnect();
  }
}

// Our test type comes with the database environment, so each test can use a "table" argument.
export const test = folio.test.extend(new DatabaseEnv());

// Run our tests.
test.runWith({ tag: 'database' });

In this example we see that tests use an environment that provides arguments to the test.

Folio uses worker processes to run test files. You can specify the maximum number of workers using --workers command line option. By using beforeAll and afterAll methods, environment can set up expensive resources to be shared between tests in each worker process. Folio will reuse the worker process for as many test files as it can, provided their environments match.

Annotations

Unfortunately, tests do not always pass. Folio supports test annotations to deal with failures, flakiness and tests that are not yet ready.

test('basic', async ({ table }) => {
  test.skip(version == 'v2', 'This test crashes the database in v2, better not run it.');
  // Test goes here.
});

test('can insert multiple rows', async ({ table }) => {
  test.fail('Broken test, but we should fix it!');
  // Test goes here.
});

Annotations may be conditional, in which case they only apply when the condition is truthy. Annotations may depend on test arguments. There could be multiple annotations on the same test, possibly in different configurations.

Possible annotations include:

skip marks the test as irrelevant. Folio does not run such a test. Use this annotation when the test is not applicable in some configuration.
fail marks the test as failing. Folio will run this test and ensure it does indeed fail. If the test does not fail, Folio will complain.
fixme marks the test as failing. Folio will not run this test, as opposite to the fail annotation. Use fixme when running the test is slow or crashy.
slow marks the test as slow and triples the test timeout.

Flaky tests

Folio deals with flaky tests with retries. Pass the maximum number of retries when running the tests, or set them in the configuration file.

npx folio --retries=3

Failing tests will be retried multiple times until they pass, or until the maximum number of retries is reached. Folio will report all tests that failed at least once:

Running 1 test using 1 worker
××±
1 flaky
  1) my.test.js:1:1

Command line

Just point Folio to your configuration file.

$ npx folio --config=my.config.ts

Arguments passed to npx folio are treated as a filter for test files. For example, npx folio my-spec will only run tests from files with my-spec in the name.

Below is a list of command line options:

--config <file>: Configuration file. Defaults to folio.config.ts or folio.config.js in the current directory.
--forbid-only: Whether to disallow test.only exclusive tests. Useful on CI. Overrides config.forbidOnly option from the configuration file.
--global-timeout <number>: Total timeout in milliseconds for the whole test run. By default, there is no global timeout. Overrides config.globalTimeout option from the configuration file.
--grep <grep> or -g <grep>: Only run tests matching this regular expression, for example /my.*test/i or my-test. Overrides config.grep option from the configuration file.
--help: Display help.
--list: List all the tests, but do not run them.
--max-failures <N> or -x: Stop after the first N test failures. Passing -x stops after the first failure. Overrides config.maxFailures option from the configuration file.
--output <dir>: Directory for artifacts produced by tests, defaults to test-results. Overrides config.outputDir option from the configuration file.
--quiet: Whether to suppress stdout and stderr from the tests. Overrides config.quiet option from the configuration file.
--repeat-each <number>: Specifies how many times to run each test. Defaults to one. Overrides config.repeatEach option from the configuration file.
--reporter <reporter>. Specify reporter to use, comma-separated, can be some combination of dot, json, junit, line, list and null. See reporters for more information.
--retries <number>: The maximum number of retries for each flaky test, defaults to zero (no retries). Overrides config.retries option from the configuration file.
--shard <shard>: Shard tests and execute only selected shard, specified in the form current/all, 1-based, for example 3/5. Overrides config.shard option from the configuration file.
--snapshot-dir <dir>: Snapshots directory, relative to tests directory. Defaults to __snapshots__. Overrides config.snapshotDir option from the configuration file.
--tag <tag...>: Only run tests tagged with one of the specified tags. Defaults to running all available tags that are defined in the configuration file.
--test-dir <dir>: Directory where Folio should search for tests, defaults to current directory. Only files matching --test-match are recognized as test files. Overrides config.testDir option from the configuration file.
--test-ignore <pattern>: Pattern used to ignore test files, defaults to node_modules. Either a regular expression (for example, /node_modules/) or a glob pattern (for example, **/ignore-dir/*). Overrides config.testIgnore option from the configuration file.
--test-match <pattern>: Pattern used to find test files, defaults to files ending with .spec.js, .test.js, .spec.ts or .test.ts. Either a regular expression (for example, /my-test-\d+/i) or a glob pattern (for example, ?(*.)+(spec|test).[jt]s). Overrides config.testMatch option from the configuration file.
--timeout <number>: Maximum timeout in milliseconds for each test, defaults to 10 seconds. Overrides config.timeout option from the configuration file.
--update-snapshots or -u: Whether to update snapshots with actual results instead of comparing them. Use this when snapshot expectations have changed. Overrides config.updateSnapshots option from the configuration file.
--workers <workers> or -j <workers>: The maximum number of concurrent worker processes. Overrides config.workers option from the configuration file.

Snapshots

Folio includes the ability to produce and compare snapshots. For that, use expect().toMatchSnapshot(). Folio auto-detects the content type, and includes built-in matchers for text, png and jpeg images, and arbitrary binary data.

test('my test', async () => {
  const image = await produceSomePNG();
  expect(image).toMatchSnapshot('optional-snapshot-name.png');
});

Snapshots are stored under __snapshots__ directory by default, configurable via command line or configuration object.

Parallelism and sharding

Folio runs tests in parallel by default, using multiple worker processes.

Workers

Each worker process creates a new environment to run tests. Different environments always run in different workers. By default, Folio reuses the worker as much as it can to make testing faster, but it will create a new worker when retrying tests, after any test failure, to initialize a new environment, or just to speed up test execution if the worker limit is not reached.

The maximum number of worker processes is controlled via command line or configuration object.

Each worker process is assigned a unique sequential index that is accessible through workerInfo object.

Shards

Folio can shard a test suite, so that it can be executed on multiple machines. For that, pass --shard=x/y to the command line. For example, to split the suite into three shards, each running one third of the tests:

$ npx folio --shard=1/3
$ npx folio --shard=2/3
$ npx folio --shard=3/3

Advanced configuration

Configuration object

Configuration file uses setConfig function to provide a global configuration to Folio. It may contain the following properties:

forbidOnly: boolean - Whether to disallow test.only exclusive tests. Useful on CI. Overridden by --forbid-only command line option.
globalTimeout: number - Total timeout in milliseconds for the whole test run. Overridden by --global-timeout command line option.
grep: RegExp | RegExp[] - Patterns to filter tests based on their title. Overridden by --grep command line option.
maxFailures: number - Stop testing after reaching the maximum number of failures. Overridden by --max-failures command line option.
outputDir: string - Directory to place any artifacts produced by tests. Overridden by --output command line option.
quiet: boolean - Whether to suppress stdout and stderr from the tests. Overridden by --quiet command line option.
repeatEach: number - Each test will be repeated multiple times. Overridden by --repeat-each command line option.
retries: number - Maximum number of retries. Overridden by --retries command line option.
shard: { total: number, current: number } | null - Shard information. Overridden by --shard command line option.
snapshotDir: string - Snapshots directory, relative to tests directory. Overridden by --snapshot-dir command line option.
testDir: string - Directory where Folio should search for tests. Overridden by --test-dir command line option.
testIgnore: string | RegExp | (string | RegExp)[] - Patterns to ignore test files. Overridden by --test-ignore command line option.
testMatch: string | RegExp | (string | RegExp)[] - Patterns to match test files. Overridden by --test-match command line option.
timeout: number - Test timeout in milliseconds. Overridden by --timeout command line option.
updateSnapshots: boolean - Whether to update snapshots instead of comparing them. Overridden by --update-snapshots command line option.
workers: number - The maximum number of concurrent worker processes. Overridden by --workers command line option.

// folio.config.ts

import * as folio from 'folio';

folio.setConfig({
  // Typically, you'd place folio.config.ts in the tests directory.
  testDir: __dirname,
  // 20 seconds per test.
  timeout: 20000,
  // Forbid test.only on CI.
  forbidOnly: !!process.env.CI,
  // Two retries for each test.
  retries: 2,
});

Changing the timeout

There are a few ways to change the test timeout - the amount of time in milliseconds per each test. Passing a zero timeout in any of these disables the timeout.

Using setConfig and passing a timeout property.

setConfing({
  testDir: __dirname,
  // Each test gets 5 seconds.
  timeout: 5000,
});

Using --timeout command line option.

# Disable timeout for all tests, e.g. for debugging.
$ npx folio --config=config.ts --timeout=0

Calling test.setTimeout(milliseconds) from the test itself.

test('my test', async () => {
  // Give this test 5 seconds.
  test.setTimeout(5000);
});

Calling test.slow() to triple the timeout.

test('my test', async () => {
  test.slow('this dataset is too large');
});

workerInfo

Depending on the configuration and failures, Folio might use different number of worker processes to run all the tests. For example, Folio will always start a new worker process after a failing test.

Environment and hooks receive workerInfo in the beforeAll and afterAll calls. The following information is accessible from the workerInfo:

config - Configuration object.
workerIndex: number - A unique sequential index assigned to the worker process.

Consider an example where we run a new http server per worker process, and use workerIndex to produce a unique port number:

import * as http from 'http';

class ServerEnv {
  server: http.Server;

  async beforeAll(workerInfo) {
    this.server = http.createServer();
    this.server.listen(9000 + workerInfo.workerIndex);
    await new Promise(ready => this.server.once('listening', ready));
  }

  async beforeEach() {
    // Provide the server as a test argument.
    return { server: this.server };
  }

  async afterAll() {
    await new Promise(done => this.server.close(done));
  }
}

testInfo

Environment and hooks receive testInfo in the beforeEach and afterEach calls. It is also available to the test function as a second parameter.

In addition to everything from the workerInfo, the following information is accessible before and during the test:

title: string - Test title.
file: string - Full path to the test file.
line: number - Line number of the test declaration.
column: number - Column number of the test declaration.
fn: Function - Test body function.
repeatEachIndex: number - The sequential repeat index.
retry: number - The sequential number of the test retry (zero means first run).
expectedStatus: 'passed' | 'failed' | 'timedOut' - Whether this test is expected to pass, fail or timeout.
timeout: number - Test timeout.
annotations - Annotations that were added to the test.
data: object - Any additional data that you'd like to attach to the test, it will appear in the report.
snapshotPathSegment: string - Relative path, used to locate snapshots for the test.
snapshotPath(...pathSegments: string[]) - Function that returns the full path to a particular snapshot for the test.
outputDir: string - Absolute path to the output directory for this test run.
outputPath(...pathSegments: string[]) - Function that returns the full path to a particular output artifact for the test.

The following information is accessible after the test body has finished, in afterEach:

duration: number - test running time in milliseconds.
status: 'passed' | 'failed' | 'timedOut' - the actual test result.
error - any error thrown by the test body.
stdout: (string | Buffer)[] - array of stdout chunks collected during the test run.
stderr: (string | Buffer)[] - array of stderr chunks collected during the test run.

Here is an example test that saves some information:

test('my test needs a file', async ({ table }, testInfo) => {
  // Do something with the table...
  // ... and then save contents.
  const filePath = testInfo.outputPath('table.dat');
  await table.saveTo(filePath);
});

Here is an example environment that automatically saves debug logs when the test fails:

import * as debug from 'debug';
import * as fs from 'fs';

class LogEnv {
  async beforeEach() {
    this.logs = [];
    debug.log = (...args) => this.logs.push(args.map(String).join(''));
    debug.enable('mycomponent');
  }

  async afterEach(testInfo) {
    if (testInfo.status !== testInfo.expectedStatus)
      fs.writeFileSync(testInfo.outputPath('logs.txt'), this.logs.join('\n'), 'utf8');
  }
}

Multiple test types and configurations

Often times there is a need for different kinds of tests, for example generic tests that use a database table, or some specialized tests that require more elaborate setup. It is also common to run tests in multiple configurations. Folio allows you to configure everything by writing code for maximum flexibility.

Instead of using test.extend() to add an environment right away, we use test.declare() to declare the test arguments and test.runWith() to give it the actual environment and configuration.

// folio.config.ts

import * as folio from 'folio';
import * as fs from 'fs';

// 20 seconds timeout, 3 retries by default.
folio.setConfig({ testDir: __dirname, timeout: 20000, retries: 3 });

// Environment with some test value.
class MockedEnv {
  async beforeEach() {
    return { value: 'some test value' };
  }
}

// Another environment that reads from a file.
class FileEnv {
  constructor() {
    this.value = fs.readFileSync('data.txt', 'utf8');
  }
  async beforeEach() {
    return { value: this.value };
  }
}

// Our tests need a common string value.
const valueTest = folio.test.declare<{ value: string }>();

// Now declare as many test types as we'd like.

// Run generic tests with two different environments and no specific configuration.
export const test = valueTest.declare();
test.runWith(new MockedEnv());
test.runWith(new FileEnv());

// Run slow tests with increased timeout, in a single environment.
export const slowTest = valueTest.declare();
slowTest.runWith(new MockedEnv(), { timeout: 100000 });

// Run smoke tests without retries - these must not be flaky.
// Adding a tag allows to run just the smoke tests with `npx folio --tag=smoke`.
export const smokeTest = valueTest.declare();
smokeTest.runWith(new MockedEnv(), { retries: 0, tag: 'smoke' });

// These tests also get a "foo" argument.
export const fooTest = valueTest.extend({
  beforeEach() {
    return { foo: 42 };
  }
});
// Although we already added the environment that gives "foo", we still have to provide
// the "value" declared in valueTest.
fooTest.runWith(new MockedEnv(), { tag: 'foo' });

We can now use our test types to write tests:

// some.spec.ts

import { test, slowTest, smokeTest, fooTest } from './folio.config';

test('just a test', async ({ value }) => {
  // This test will be retried.
  expect(value).toBe('wrong value');
});

slowTest('does a lot', async ({ value }) => {
  for (let i = 0; i < 100000; i++)
    expect(value).toBe('some test value');
});

smokeTest('a smoke test', async ({ value }) => {
  // This test will not be retried.
  expect(value).toBe('some test value');
});

fooTest('a smoke test', async ({ foo }) => {
  // Note the different test arguments.
  expect(foo).toBe(42);
});

Global setup and teardown

To set something up once before running all tests, use globalSetup hook in the configuration file. Similarly, use globalTeardown to run something once after all the tests.

// folio.config.ts

import * as folio from 'folio';
import * as app from '../my-app';
import * as http from 'http';

let server: http.Server;

folio.globalSetup(async () => {
  server = http.createServer(app);
  await new Promise(done => server.listen(done));
  process.env.SERVER_PORT = String(server.address().port); // Expose port to the tests.
});

folio.globalTeardown(async () => {
  await new Promise(done => server.close(done));
});

folio.setConfig({ testDir: __dirname });
export const test = folio.newTestType();
test.runWith();

Test options

It is common for test environment to be configurable, based on various test needs. There are three different ways to configure environment in Folio, depending on the usecase.

Creating multiple environment instances

Use this method when you need to run tests in multiple configurations. See Multiple test types and configurations for more details.

// folio.config.ts

import * as folio from 'folio';

folio.setConfig({ testDir: __dirname });

// This environment provides a "hello".
class HelloEnv {
  constructor(name) {
    this.name = name;
  }

  async beforeEach() {
    return { hello: `Hello, ${this.name}!` };
  }
}

// Tests expect a "hello" value.
export const test = folio.test.declare<{ hello: string }>();

// Now, run tests in two configurations.
test.runWith(new HelloEnv('world'));
test.runWith(new HelloEnv('test'));

Providing function as a test argument

Use this method when you need to alter the environment for some tests.

Define the function provided by environment. In our case, this will be createHello function.

// folio.config.ts

import * as folio from 'folio';

folio.setConfig({ testDir: __dirname });

// This environment provides a function "createHello".
class CreateHelloEnv {
  async beforeEach() {
    return { createHello: (name: string) => `Hello, ${name}!` };
  }
}

// Tests get a "createHello" function.
export const test = folio.test.extend(new CreateHelloEnv());
test.runWith();

Now use this function in the test.

// some.spec.ts

import { test } from './folio.config';
import { expect } from 'folio';

test('my test', ({ createHello }) => {
  expect(createHello('world')).toBe('Hello, world!');
});

Specifying options with `test.useOptions`

Use this method when you have common configuration that needs to often change between tests.

// folio.config.ts

import * as folio from 'folio';

folio.setConfig({ testDir: __dirname });

// This environment provides a "hello".
class HelloEnv {
  // Declare the TestOptions type.
  testOptionsType(): { name?: string } {
    return {} as any;  // It does not matter what you return from here.
  }

  // Use TestOptions in beforeEach.
  async beforeEach({ name }, testInfo: folio.TestInfo) {
    // Don't forget to account for missing "name".
    return { hello: `Hello, ${name || ''}!` };
  }
}

// Tests expect a "hello" value, and can provide a "name" option.
export const test = folio.test.extend(new HelloEnv());
test.runWith();

Now specify the options in the test file with test.useOptions. It works for each test in the file, or the containing test.describe block if any, similar to test.beforeEach and other hooks.

// some.spec.ts

import { test } from './folio.config';
import { expect } from 'folio';

test.useOptions({ name: 'world' });
test('my test with options', ({ hello }) => {
  expect(hello).toBe('Hello, world!');
});
test('another test, same options', ({ hello }) => {
  expect(hello).toBe('Hello, world!');
});

test.describe('this suite uses different options', () => {
  test.useOptions({ name: 'test' });
  test('different options', ({ hello }) => {
    expect(hello).toBe('Hello, test!');
  });
});

Reporters

Folio comes with a few built-in reporters for different needs and ability to provide custom reporters. The easiest way to try out built-in reporters is --reporter command line option.

$ npx folio --config=config.ts --reporter=list

For more control, you can specify reporters programmatically in the configuration file.

// folio.config.ts

import * as folio from 'folio';

// A long list of tests for the terminal.
folio.setReporters([ new folio.reporters.list() ]);

if (process.env.CI) {
  // Entirely different config on CI.
  // Use very concise "dot" reporter plus a comprehensive json report.
  folio.setReporters([
    new folio.reporters.dot(),
    new folio.reporters.json({ outputFile: 'test-results.json' }),
  ]);
}

Built-in reporters

All built-in reporters show detailed information about failures, and mostly differ in verbosity for successful runs.

Line reporter

Line reporter is default. It uses a single line to report last finished test, and prints failures when they occur. Line reporter is useful for large test suites where it shows the progress but does not spam the output by listing all the tests. Use it with --reporter=line or new folio.reporters.line().

Here is an example output in the middle of a test run. Failures are reporter inline.

$ npm run test -- --reporter=line
Running 124 tests using 6 workers
  1) dot-reporter.spec.ts:20:1 › render expected ===================================================

    Error: expect(received).toBe(expected) // Object.is equality

    Expected: 1
    Received: 0

[23/124] gitignore.spec.ts - should respect nested .gitignore

List reporter

List reporter is verbose - it prints a line for each test being run. Use it with --reporter=list or new folio.reporters.list().

Here is an example output in the middle of a test run. Failures will be listed at the end.

$ npm run test -- --reporter=list
Running 124 tests using 6 workers

  ✓ should access error in env (438ms)
  ✓ handle long test names (515ms)
  x 1) render expected (691ms)
  ✓ should timeout (932ms)
    should repeat each:
  ✓ should respect enclosing .gitignore (569ms)
    should teardown env after timeout:
    should respect excluded tests:
  ✓ should handle env beforeEach error (638ms)
    should respect enclosing .gitignore:

Dot reporter

Dot reporter is very concise - it only produces a single character per successful test run. It is useful on CI where you don't want a lot of output. Use it with --reporter=dot or new folio.reporters.dot().

Here is an example output in the middle of a test run. Failures will be listed at the end.

$ npm run test -- --reporter=dot
Running 124 tests using 6 workers
······F·············································

JSON reporter

JSON reporter produces an object with all information about the test run. It is usually used together with some terminal reporter like dot or line.

You would usually want to output JSON into a file. When running with --reporter=json, use FOLIO_JSON_OUTPUT_NAME environment variable:

$ FOLIO_JSON_OUTPUT_NAME=results.json npm run test -- --reporter=json,dot

With setReporters call, pass options to the constructor:

folio.setReporters([
  new folio.reporters.json({ outputFile: 'results.json' })
]);

JUnit reporter

JUnit reporter produces a JUnit-style xml report. It is usually used together with some terminal reporter like dot or line.

You would usually want to output into an xml file. When running with --reporter=junit, use FOLIO_JUNIT_OUTPUT_NAME environment variable:

$ FOLIO_JUNIT_OUTPUT_NAME=results.xml npm run test -- --reporter=junit,line

With setReporters call, pass options to the constructor:

folio.setReporters([
  new folio.reporters.junit({ outputFile: 'results.xml' })
]);

Expect

Add custom matchers using expect.extend

Folio uses expect under the hood which has the functionality to extend it with custom matchers. See the following example where a custom toBeWithinRange function gets added.

folio.config.ts

import * as folio from 'folio';

folio.setConfig({ testDir: __dirname, timeout: 30 * 1000 });

folio.expect.extend({
  toBeWithinRange(received: number, floor: number, ceiling: number) {
    const pass = received >= floor && received <= ceiling;
    if (pass) {
      return {
        message: () => 'passed',
        pass: true,
      };
    } else {
      return {
        message: () => 'failed',
        pass: false,
      };
    }
  },
});

folio.test.runWith();

example.spec.ts

import { expect, test } from 'folio';

test('numeric ranges', () => {
  expect(100).toBeWithinRange(90, 110);
  expect(101).not.toBeWithinRange(0, 100);
});

global.d.ts

declare namespace folio {
  interface Matchers<R> {
    toBeWithinRange(a: number, b: number): R;
  }
}

To import expect matching libraries like jest-extended you can import it from your globals.d.ts:

import 'jest-extended';

pratiksharma23 / folio

Folio

Docs

Isolation and flexibility

Writing a test

Writing a configuration file

Creating an environment

Annotations

Flaky tests

Command line

Snapshots

Parallelism and sharding

Workers

Shards

Advanced configuration

Configuration object

Changing the timeout

workerInfo

testInfo

Multiple test types and configurations

Global setup and teardown

Test options

Creating multiple environment instances

Providing function as a test argument

Specifying options with `test.useOptions`

Reporters

Built-in reporters

Line reporter

List reporter

Dot reporter

JSON reporter

JUnit reporter

Expect

Add custom matchers using expect.extend

About

Languages

Folio

Docs

Isolation and flexibility

Writing a test

Writing a configuration file

Creating an environment

Annotations

Flaky tests

Command line

Snapshots

Parallelism and sharding

Workers

Shards

Advanced configuration

Configuration object

Changing the timeout

workerInfo

testInfo

Multiple test types and configurations

Global setup and teardown

Test options

Creating multiple environment instances

Providing function as a test argument

Specifying options with test.useOptions

Reporters

Built-in reporters

Line reporter

List reporter

Dot reporter

JSON reporter

JUnit reporter

Expect

Add custom matchers using expect.extend

About

Languages

Specifying options with `test.useOptions`