The integration tests from core are not guaranteed to pass once extensions are loaded, since they can have arbitrary side-effects on core functions via hooks.
For example, installing Scribunto makes core integration tests fail, because (among other things) one of the tests enumerates all the registered namespaces, and Scribunto adds the 'Module' and 'Module_talk' namespaces.
For this reason, integration-config only runs extension tests and core *unit tests* when extensions are installed.
But Parsoid at this moment is running the full test suite including integration tests.