Proposed changes

Allow running Multiremote in parallel by passing an array of multiremote capabilities - #5445
So that something like this is possible:

capabilities: [
        {
            browser1: { capabilities: { browserName: 'chrome' } },
            browser2: { capabilities: { browserName: 'chrome' } }
        },
        {
            browser1: { capabilities: { browserName: 'firefox' } },
            browser2: { capabilities: { browserName: 'firefox' } }
        },
        {
            browser1: { capabilities: { browserName: 'chrome' } },
            browser2: { capabilities: { browserName: 'firefox' } }
        }
    ],

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Checklist

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• I have added proper type definitions for new commands (if appropriate)

Further comments

As I see it, there is no problem for runner to execute multiple Multiremote sessions in parallel. It can be accomplished by simply pushing multiple tests into @wdio/cli/launcher.js's schedule array. The main problem is getting capabilities there in correct format, which is a little problematic because all of services are made to only support array as singleremote and object as multiremote.

Here in these changes I have modified @wdio/selenium-standalone-service to also handle multiremote array, which has to be done everywhere if this change makes sense.

To use parallel multiremote, capabilities can be passed like this:

parallelMultiremote: true,
capabilities: [
    {
        browser1: { capabilities: { browserName: 'chrome' } },
        browser2: { capabilities: { browserName: 'chrome' } }
    },
    {
        browser1: { capabilities: { browserName: 'firefox' } },
        browser2: { capabilities: { browserName: 'firefox' } }
    }
],

Here you can see a new test runner option parallelMultiremote. When it's absent/false, capabilities will be treated just like before but when it's true, it will use new logic. This is the way which resulted in least changes needed for it to work.

I have only tested in one simple case and it worked very well, but there is something probably broken by this.

Reviewers: @webdriverio/project-committers