Implement test coverage

Started the work here. Need to actually run the tests in Gitlab CI, but locally am getting the following to pass:

$ ../vendor/bin/phpunit modules/contrib/jsonapi_permission_access/tests/src/Functional/JsonApiPermissionAccessTest.php --verbose -c ./core/phpunit.xml.dist
PHPUnit 9.6.19 by Sebastian Bergmann and contributors.

Runtime:       PHP 8.2.15
Configuration: ./core/phpunit.xml.dist

Testing Drupal\Tests\jsonapi_permission_access\JsonApiPermissionAccessTest\JsonApiPermissionAccessTest
.                                                                   1 / 1 (100%)

Time: 00:04.327, Memory: 4.00 MB

OK (1 test, 10 assertions)

Resource: https://www.drupal.org/docs/develop/git/using-gitlab-to-contribute-to-dr... →