nixos/mailcatcher: add nixos test

nixos/tests/all-tests.nix

@@ -131,6 +131,7 @@ in
   #lightdm = handleTest ./lightdm.nix {};
   login = handleTest ./login.nix {};
   #logstash = handleTest ./logstash.nix {};
+  mailcatcher = handleTest ./mailcatcher.nix {};
   mathics = handleTest ./mathics.nix {};
   matrix-synapse = handleTest ./matrix-synapse.nix {};
   memcached = handleTest ./memcached.nix {};

nixos/tests/mailcatcher.nix

@@ -0,0 +1,26 @@
+import ./make-test.nix ({ lib, ... }:
+
+{
+  name = "mailcatcher";
+  meta.maintainers = [ lib.maintainers.aanderse ];
+
+  machine =
+    { pkgs, ... }:
+    {
+      services.mailcatcher.enable = true;
+
+      networking.defaultMailServer.directDelivery = true;
+      networking.defaultMailServer.hostName = "localhost:1025";
+
+      environment.systemPackages = [ pkgs.mailutils ];
+    };
+
+  testScript = ''
+    startAll;
+
+    $machine->waitForUnit('mailcatcher.service');
+    $machine->waitForOpenPort('1025');
+    $machine->succeed('echo "this is the body of the email" | mail -s "subject" root@example.org');
+    $machine->succeed('curl http://localhost:1080/messages/1.json') =~ /this is the body of the email/ or die;
+  '';
+})