When wireguard began being tested on multiple kernel versions, the
current default version at the time was hard coded:
41bd6d2614.
We should update this and prevent it from becoming stale ever again by
computing the default value.
When testing WireGuard updates, I usually run the VM-tests with
different kernels to make sure we're not introducing accidental
regressions for e.g. older kernels.
I figured that we should automate this process to ensure continuously
that WireGuard works fine on several kernels.
For now I decided to test the latest LTS version (5.4) and
the latest kernel (currently 5.6). We can add more kernels in the
future, however this seems to significantly slow down evaluation and
time.
The list can be customized by running a command like this:
nix-build nixos/tests/wireguard --arg kernelVersionsToTest '["4.19"]'
The `kernelPackages` argument in the tests is null by default to make
sure that it's still possible to invoke the test-files directly. In that
case the default kernel of NixOS (currently 5.4) is used.
After working on the last wireguard bump (#57534), we figured that it's
probably a good idea to have a basic test which confirms that a simple
VPN with wireguard still works.
This test starts two peers with a `wg0` network interface and adds a v4
and a v6 route that goes through `wg0`.
