gen.js

var webdriverio = require('webdriverio'),
    assert      = require('assert'),
    client      = {},
    url         = 'http://google.com';

client = webdriverio.remote(
    {
        desiredCapabilities: {browserName: 'chrome'},
        logLevel: 'verbose'
    }
);

client.addCommand('testCommand', function() {
    console.log(url);
    return this.windowHandleSize({width: 1920, height: 1080})
        .url(url)
        .waitForExist('.gsfi', 10000)
        .pause(2000)
        .addValue('.gsfi', 'testtesttest');
});

// expose revised client object
module.exports = {
    client: client
};

wdio.conf.js

exports.config = {

    //
    // ==================
    // Specify Test Files
    // ==================
    // Define which test specs should run. The pattern is relative to the location of this
    // file.
    //
    specs: [
        // './tests/test_*.js'
        './wdiotest.js'
    ],
    // Patterns to exclude.
    exclude: [
        // 'path/to/excluded/files'
    ],
    //
    // ============
    // Capabilities
    // ============
    // Define your capabilities here. WebdriverIO can run multiple capabilties at the same
    // time. Depending on the number of capabilities WebdriverIO launches several test
    // sessions. Within your capabilities you can overwrite the spec and exclude option in
    // order to group specific specs to a specific capability.
    //
    // If you have trouble getting all important capabilities together check out Sauce Labs
    // platform configurator. A great tool to configure your capabilities.
    // https://docs.saucelabs.com/reference/platforms-configurator
    //
    capabilities: [{
        browserName: 'chrome'
    }],
    //
    // ===================
    // Test Configurations
    // ===================
    // Define all options that are relevant for the WebdriverIO instance here
    //
    // Level of logging verbosity.
    logLevel: 'verbose',
    //
    // Enables colors for log output
    coloredLogs: true,
    //
    // Saves a screenshot to a given path if a command fails.
    screenshotPath: './errorShots/',
    //
    // Shorten url command calls by setting a base url. If your url parameter starts with "/"
    // the base url gets prepended.
    // baseUrl: 'http://localhost',
    //
    // Default timeout for all waitForXXX commands.
    waitforTimeout: 10000,
    //
    // Initialise the browser instance with a WebdriverIO plugin. The object should have the
    // plugin name as key and the desired plugin options as property. Make sure you have
    // the plugin installed before running any tests. The following plugins are currently
    // available:
    // WebdriverCSS: https://github.com/webdriverio/webdrivercss
    // WebdriverRTC: https://github.com/webdriverio/webdriverrtc
    // Browserevent: https://github.com/webdriverio/browserevent
    // plugins: {
    //     webdrivercss: {
    //         screenshotRoot: 'my-shots',
    //         failedComparisonsRoot: 'diffs',
    //         misMatchTolerance: 0.05,
    //         screenWidth: [320,480,640,1024]
    //     },
    //     webdriverrtc: {},
    //     browserevent: {}
    // },
    //
    // Framework you want to run your specs with.
    // The following are supported: mocha, jasmine and cucumber
    // see also: http://webdriver.io/guide/testrunner/frameworks.html
    //
    // Make sure you have the node package for the specific framework installed before running
    // any tests. If not please install the following package:
    // Mocha: `$ npm install mocha`
    // Jasmine: `$ npm install jasmine`
    // Cucumber: `$ npm install cucumber`
    framework: 'mocha',
    //
    // Test reporter for stdout.
    // The following are supported: dot (default), spec and xunit
    // see also: http://webdriver.io/guide/testrunner/reporters.html
    reporter: 'xunit',

    //
    // Some reporter require additional information which should get defined here
    reporterOptions: {
        //
        // If you are using the "xunit" reporter you should define the directory where
        // WebdriverIO should save all unit reports.
        outputDir: './'
    },

    //
    // =====
    // Hooks
    // =====
    // Run functions before or after the test. If one of them return with a promise, WebdriverIO
    // will wait until that promise got resolved to continue.
    // see also: http://webdriver.io/guide/testrunner/hooks.html
    //
    // Gets executed before all workers get launched.
    onPrepare: function() {
        // do something
    },
    //
    // Gets executed before test execution begins. At this point you will have access to all global
    // variables like `browser`. It is the perfect place to define custom commands.
    before: function() {
        // do something
    },
    //
    // Gets executed after all tests are done. You still have access to all global variables from
    // the test.
    after: function() {
        // do something
    },
    //
    // Gets executed after all workers got shut down and the process is about to exit. It is not
    // possible to defer the end of the process using a promise.
    onComplete: function() {
        // do something
    }
};

wdiotest.js

var assert      = require('assert'),
    browser     = require('./gen').client,
    mocha       = require('mocha'),
    _           = require('underscore');

describe('test suite', function() {
    it('should work', function() {
        browser
            // .url('http://google.com')
            .testCommand()
            .waitForExist('body', 10000)
            .saveScreenshot('wow.png');
    });
});