mailhog: add simple test

nixos/tests/all-tests.nix

@@ -210,6 +210,7 @@ in
   magic-wormhole-mailbox-server = handleTest ./magic-wormhole-mailbox-server.nix {};
   magnetico = handleTest ./magnetico.nix {};
   mailcatcher = handleTest ./mailcatcher.nix {};
+  mailhog = handleTest ./mailhog.nix {};
   mariadb-galera-mariabackup = handleTest ./mysql/mariadb-galera-mariabackup.nix {};
   mariadb-galera-rsync = handleTest ./mysql/mariadb-galera-rsync.nix {};
   matomo = handleTest ./matomo.nix {};

nixos/tests/mailhog.nix

@@ -0,0 +1,24 @@
+import ./make-test-python.nix ({ lib, ... }: {
+  name = "mailhog";
+  meta.maintainers = with lib.maintainers; [ jojosch ];
+
+  machine = { pkgs, ... }: {
+    services.mailhog.enable = true;
+
+    environment.systemPackages = with pkgs; [ swaks ];
+  };
+
+  testScript = ''
+    start_all()
+
+    machine.wait_for_unit("mailhog.service")
+    machine.wait_for_open_port("1025")
+    machine.wait_for_open_port("8025")
+    machine.succeed(
+        'echo "this is the body of the email" | swaks --to root@example.org --body - --server localhost:1025'
+    )
+    assert "this is the body of the email" in machine.succeed(
+        "curl --fail http://localhost:8025/api/v2/messages"
+    )
+  '';
+})