(PUP-1177) update ParsedFile provider unit tests

The constructor for the :flat filetype accepts a second argument now.
This second argument must be taken into account when stubbing specific
invocations.
(PUP-1177) restore :ram FileType compatibility

The :ram filetype, as an alternative to :flat, is often used for spectests
of ParsedFile providers. The providers normally use the :flat type, but through
mocking, are made to use :ram in test context. Since the providers often pass
both supported arguments to the :flat constructor, it must be accepted by the
constructor of the :ram type as well.