Testing the frontend behavior in functional tests creates currently an own PHP sub-request to execute TypoScript in frontent context.
Several hooks collect called cObjects and try to find the correct nesting levels. Albeit this is working for the current tests, it is way too complex for extending the tests for further scenarios like for FAL and Extbase.
The hook magic is resolved and explicit render functions, called via TypoScript, collect the data an output aggregated JSON data in the end.
Besides that the PHP sub-request execution now re-uses the PHPUnit utilities to determine and run the accordant executables.