The EditSubpages extension restricts anonymous users from editing most pages. As such as the webdriver.io spec tests in mediawiki/core fail due to a permission error. https://www.mediawiki.org/wiki/Extension:EditSubpages
User ✓ should be able to create account ✓ should be able to log in ✓ should be able to change preferences 1) Page should be creatable: An element could not be located on the page using the given search parameters ("#wpTextbox1"). 2) Page should be re-creatable: An element could not be located on the page using the given search parameters ("#wpTextbox1"). 3) Page should be editable: invalid element state: Element must be user-editable in order to clear it.
Assuming the extensions tests are run first and that we have admin rights on the wiki, we should be able to whitelist a few pages to allow edition. The wiki page mentions whitelisting them in [[MediaWiki:Unlockedpages]].
See also T196960 which is to let some extensions opt out of running webdriver.io tests.