this test fails with

[FOS\HttpCache\Exception\MissingHostException] 
Path "path=http://example.com/my/path" cannot be invalidated without a host. Either invalidate full URLs containing hostnames instead of paths or configure the caching proxy class with a hostname. 

so it seems the functional test setup does not have a default host. but more severe, something about our host handling seems broken. this is surprising me, as i think we covered that all by lots of tests...