Uncaught PHP Exception Drupal\Core\Config\Schema\SchemaIncompleteException: "Schema errors for optimizely.settings with the following errors: optimizely.settings:langcode missing schema" at /var/www/html/opti/core/lib/Drupal/Core/Config/Testing/ConfigSchemaChecker.php line 98In this message, optimizely.settings is the name of a group of configuration settings. It is also a configuration key in a .schema.yml file that is required for automated testing, which I blogged about earlier at Beta 3 --> Beta 4: Configuration schema and metadata.
The article Fix config schema mentioned a very similar error message and stated "Because of a recent core change all tests are failing". I looked at the patches in that article, but I could not figure out what needed to be added in our case.
Then a search through the core code for the string "langcode:" led me to add langcode: as a key to the .schema.yml file as in the following.
label: 'Optimizely Config Data'
label: 'Optimizely ID Number'
label: 'Language code'
Problem solved. All automated tests passed after this change.
Update: Also see my later post on Module: Configuration Inspector for Drupal 8.
Beta 3 --> Beta 4: Configuration schema and metadata
Fix config schema
All TestBase derived tests now enforce strict configuration schema adherence by default