BrowserTestBase::initMink crashes if not using DrupalTestBrowser

Problem/Motivation

If using a different driver instance and not DrupalTestBrowser \Drupal\Tests\BrowserTestBase::initMink crashes as it assumes the abstract browser instance has a method for setting the HTTP client.

$driver->getClient()->setClient($client); this fails.

Steps to reproduce

I was experimenting with \Symfony\Component\HttpKernel\HttpKernelBrowser.

  protected function getDefaultDriverInstance() {
    return new BrowserKitDriver(new HttpKernelBrowser(
      $this->container->get('http_kernel')
    ));
  }

but initMink crashes with this.

Proposed resolution

Verify the driver's client is instance of DrupalTestBrowser

$driver->getClient() instanceof DrupalTestBrowser

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet