Hello!
To my understanding no package that uses another -dev package as a build dependency would ever have any need for neither the examples nor testdata. Those files are more relevant to the person developing the library, right? Should we aim to remove examples/ and testdata/ in future Go libraries (*-dev packages)?
If your package has:
Testsuite: autopkgtest-pkg-go
Then ci.debian.net runs the test suite, so testdata/ is very much necessary.
Testdata might also be needed when a reverse dep of your -dev package runs its tests, not 100% sure though...
I don't know about examples/, but I'm sure it's there for a reason. Others from the team can answer more precisely.
Cheers,
Arnaud