tests/gnrc_dhcpv6_client: add script to check if $IFACE exists

[miri64]

Contribution description

Adds a checker script if the required interface for tests/gnrc_dhcpv6_client exists.

Testing procedure

Run tests/gnrc_dhcpv6_client with and without a TAP interface

sudo dist/tools/tapsetup/tapsetup
make -C tests/gnrc_dhcpv6_client flash -j test-with-config # should succeed
sudo dist/tools/tapsetup/tapsetup -d
make -C tests/gnrc_dhcpv6_client flash -j test-with-config # should fail with appropriate error message

Issues/PRs references

Depends on #16795 for the config check to work and #16796 for the $IFACE export (see #16797 (comment)).

[miri64]

As pointed out by @fjmolinas in #16796 (comment), the export is not necessary. So I removed that dependency with the latest rebase and adopted the Makefile to expose IFACE to the config checker target.

[kfessel]

PORT may be checked for existence as well - in native case

[kfessel]

I think this should be rebased and squashed -since its dependencies are merged.
Maybe the wording in the failure message can be changed as well:

[miri64]

PORT may be checked for existence as well - in native case

It is set by default.

[kfessel]

PORT may be checked for existence as well - in native case

It is set by default.

i meant check if the interface the is named by PORT is exiting (since it might be a non exiting tap interface with native)

but it is also the case the such a checkscript is not able to test for every misconfiguration (maybe both exist but aren't conected)

[miri64]

i meant check if the interface the is named by PORT is exiting (since it might be a non exiting tap interface with native)

The native instance will fail to start if it can't be used as a TAP interface or if it isn't initialized. Adding yet another check for that is IMHO really not necessary. If you don't know how to use native with networking, you shouldn't do testing ;-).

[miri64]

Rebased and squashed latest suggestion

[kfessel]

somehow IFACE sems to not be set

tests/gnrc_dhcpv6_client$ make test-with-config
Device "" does not exist.
You may be able to create "" by using e.g. `dist/tools/tapsetup/tapsetup`.
System configuration for tests is not available, check tests/gnrc_dhcpv6_client/tests-with-config/check-config.sh failed.

tests/gnrc_dhcpv6_client$ IFACE=tapbr0 make test-with-config

finishes successfully

[kfessel]

I think a comment would be nice for a future reader of this Makefile

[kfessel]

I tested:
tapbr0 missing and $ make test-with-config fails with message as expected
tapbr0 setup and $ make test-with-config succeeds as expected
tapbr1 missing and $ IFACE=tapbr1 PORT=tap10 make test-with-config fails with message as expected
tapbr1 setup and $ IFACE=tapbr1 PORT=tap10 make test-with-config succeeds as expected

in between these tests kea-dhcp6 needed to be killed since its config changed

please squash

[miri64]

please squash

Done. I also removed the now orphaned test-with-config/check-config target within the application's Makefile.

[kfessel]

🎉

[kfessel]

🎉
🥳
🎉