My guess is that you are assuming that fdroidclient is developed via the
process you use. I’m guessing it is not. I generally work by limiting
changes to specific areas for each release, that means that all aspects
of the app do not need to be tested before each release. That saves a
lot of dev and testing time. This is a common dev workflow for doing
things efficiently.
Of course, a complete, automated test suite across every device we
support would be welcome. That does not currently exist.