[strongSwan] NixOS test

[Bas van Dijk]

I've created a PR for the NixOS Linux distribution that adds a module
for strongswan-swanctl:

  https://github.com/NixOS/nixpkgs/pull/27958

Although the new module works on our company VPN I would also like to
add a NixOS test to ensure it keeps working. I've mimicked one of the
swanctl tests from the strongswan project:

  https://github.com/LumiGuide/nixpkgs/blob/strongswan-swanctl-test/nixos/tests/strongswan-swanctl.nix

Although SAs get established successfully between gateway moon and
roadwarrior carol I can't seem to ping alice from carol. Since I'm no
networking expert I'm probably missing something obvious. It would be
great if somebody could give me a tip or point me in the right
direction.

To run the test for yourself you don't need to install NixOS, you only
need the Nix package manager (which is easy to uninstall later on;
just rm -r /nix):

  $ curl https://nixos.org/nix/install | sh

Then clone my nixpkgs fork and checkout the right branch:

  $ git clone https://github.com/LumiGuide/nixpkgs.git
  $ cd nixpkgs
  $ git checkout strongswan-swanctl-test

Look in nixos/tests/strongswan-swanctl.nix to see how to run the test
but the following should get you started:

  $ nix-build nixos/tests/strongswan-swanctl.nix

Note that I also asked this question on the nix-devel mailinglist:

  https://groups.google.com/forum/#!topic/nix-devel/X-0T97MLR7I

Cheers,

Bas