No schema for my_module.global error on unit test

Question

I got an existing Drupal 8.2.x project with existing unit tests. When I run a sample unit test, I get the error (real module name redacted):

No schema for my_module.global

This doesn't seem to be related to the my_module.schema.yml file, or any DB schema that I can tell. Drilling down, I got this output for the $definition variable in \Drupal\Core\Config\TypedConfigManager.php, which the unit test calls up (among others):

array (
  'label' => 'Undefined',
  'class' => 'Drupal\\Core\\Config\\Schema\\Undefined',
  'definition_class' => '\\Drupal\\Core\\TypedData\\DataDefinition',
  'type' => 'undefined',
)

For core modules the class is Drupal\\Core\\Config\\Schema\\Mapping. Note that the error complains about a schema for my_module.global, which is one of the YAML config files for this module (can't tell how else it's related).

The question is, what does this schema mean exactly, and where do I set it for my module?

Answer 1

Turns out that it is related to the my_module.schema.yml. Looks like every YAML file under my_module/config/install must have a corresponding schema in the my_module.schema.yml file in order to set up a unit test, even if this is not actually required for the module to work. It needs to look something like this (assuming the config/install file name is my_module.global.yml):

my_module.global:
  type: mapping
  label: 'My label'
  mapping:
    property:
      type: text
      label: 'Property label'

If unsure which properties need to go there, running the unit test without them will give a list as part of the error. I'm sure there is a better way to find this, but that's the way I found so far.

Edit – the whole schema verification mechanism can be turned off: In drupal/core/lib/Drupal/Core/Test/TestSetupTrait.php, $strictConfigSchema needs to be set to FALSE.

Edit 2 – here is a module that provides a neat UI for schema validation: https://www.drupal.org/project/config_inspector