`pytest` fails for PalH5 source for new attribite `follow_links`

[dschick]

There is a weird behaviour of pytest after introducing the new attribute follow_links in the PalH5 source class.
It tries to access the attribute via __getattr__() of the parent class Source.
This obviously fails, as this attribute is not present there.

However, I do not understand why the original __getattribute__() of the PalkH5 class fails in pytest but not when normally executing the script