Custom Services

You can write your own custom service for the WDIO test runner to custom-fit your needs.

Services are add-ons that are created for reusable logic to simplify tests, manage your test suite and integrate results. Services have access to all the same hooks available in the wdio.conf.js.

There are two types of services that can be defined: a launcher service that only has access to the onPrepare, onWorkerStart, onWorkerEnd and onComplete hook which are only executed once per test run, and a worker service that has access to all other hooks and is being executed for each worker. Note that you can not share (global) variables between both types of services as worker services run in a different (worker) process.

A launcher service can be defined as follows:

export default class CustomLauncherService {
    // If a hook returns a promise, WebdriverIO will wait until that promise is resolved to continue.
    async onPrepare(config, capabilities) {
        // TODO: something before all workers launch
    }

    onComplete(exitCode, config, capabilities) {
        // TODO: something after the workers shutdown
    }

    // custom service methods ...
}

Whereas a worker service should look like this:

export default class CustomWorkerService {
    /**
     * `serviceOptions` contains all options specific to the service
     * e.g. if defined as follows:
     *
     * ```
     * services: [['custom', { foo: 'bar' }]]
     * ```
     *
     * the `serviceOptions` parameter will be: `{ foo: 'bar' }`
     */
    constructor (serviceOptions, capabilities, config) {
        this.options = serviceOptions
    }

    /**
     * this browser object is passed in here for the first time
     */
    async before(config, capabilities, browser) {
        this.browser = browser

        // TODO: something before all tests are run, e.g.:
        await this.browser.setWindowSize(1024, 768)
    }

    after(exitCode, config, capabilities) {
        // TODO: something after all tests are run
    }

    beforeTest(test, context) {
        // TODO: something before each Mocha/Jasmine test run
    }

    beforeScenario(test, context) {
        // TODO: something before each Cucumber scenario run
    }

    // other hooks or custom service methods ...
}

It is recommended to store the browser object through the passed in parameter in the constructor. Lastly expose both types of workers as following:

import CustomLauncherService from './launcher'
import CustomWorkerService from './service'

export default CustomWorkerService
export const launcher = CustomLauncherService

If you are using TypeScript and want to make sure that hook methods parameter are type safe, you can define your service class as follows:

import type { Capabilities, Options, Services } from '@wdio/types'

export default class CustomWorkerService implements Services.ServiceInstance {
    constructor (
        private _options: MyServiceOptions,
        private _capabilities: Capabilities.RemoteCapability,
        private _config: Options.Testrunner
    ) {
        // ...
    }

    // ...
}

Service Error Handling

An Error thrown during a service hook will be logged while the runner continues. If a hook in your service is critical to the setup or teardown of the test runner, the SevereServiceError exposed from the webdriverio package can be used to stop the runner.

import { SevereServiceError } from 'webdriverio'

export default class CustomServiceLauncher {
    async onPrepare(config, capabilities) {
        // TODO: something critical for setup before all workers launch

        throw new SevereServiceError('Something went wrong.')
    }

    // custom service methods ...
}

Import Service from Module

The only thing to do now in order to use this service is to assign it to the services property.

Modify your wdio.conf.js file to look like this:

import CustomService from './service/my.custom.service'

export const config = {
    // ...
    services: [
        /**
         * use imported service class
         */
        [CustomService, {
            someOption: true
        }],
        /**
         * use absolute path to service
         */
        ['/path/to/service.js', {
            someOption: true
        }]
    ],
    // ...
}

Publish Service on NPM

To make services easier to consume and discover by the WebdriverIO community, please follow these recommendations:

• Services should use this naming convention: wdio-*-service
• Use NPM keywords: wdio-plugin, wdio-service
• The main entry should export an instance of the service
• Example services: @wdio/sauce-service

Following the recommended naming pattern allows services to be added by name:

// Add wdio-custom-service
export const config = {
    // ...
    services: ['custom'],
    // ...
}

Add Published Service to WDIO CLI and Docs

We really appreciate every new plugin that could help other people run better tests! If you have created such a plugin, please consider adding it to our CLI and docs to make it easier to be found.

Please raise a pull request with the following changes:

• add your service to the list of supported services) in the CLI module
• enhance the service list for adding your docs to the official Webdriver.io page