According to implementation of the OrganizationService, some functionalities covered by the TCK could be hard or even impossible to implement. Knowing that, some unit tests can simply be disabled using system properties. See the following types of unit tests that you can disable:
Queries on users based on the login date. If you want to skip those types of unit tests, simply set the system properties orgservice.test.configuration.skipDateTests to true.
Queries on users that are not case-sensitive. If you want to skip those types of unit tests, simply set the system properties orgservice.test.configuration.skipCISearchTests to true.