Extbase translation tests don't fulfill expectations
The Extbase TranslationTest should be executed in frontend mode. A mock of the EnvironmentService is infiltrated into the GeneralUtility to be used as singleton instance. Unfortunately the whole setUpBasicFrontendEnvironment method is called after the subject (PostRepository) was initiliazed by the ObjectManager. This early initialization doesn't know the mock and generates its own EnvironmentService singleton instance.
The tests and their expectations don't use the EnvironmentServiceMock and run in another mode (backend).