nixos/tests/kea: test ctrl-agent via kea-exporter

nixos/tests/kea.nix

···
             name = "/var/lib/kea/dhcp4.leases";
           };
 
+          control-socket = {
+            socket-type = "unix";
+            socket-name = "/run/kea/dhcp4.sock";
+          };
+
           interfaces-config = {
             dhcp-socket-type = "raw";
             interfaces = [
···
             } ];
           };
         };
+      };
+
+      services.kea.ctrl-agent = {
+        enable = true;
+        settings = {
+          http-host = "127.0.0.1";
+          http-port = 8000;
+          control-sockets.dhcp4 = {
+            socket-type = "unix";
+            socket-name = "/run/kea/dhcp4.sock";
+          };
+        };
+      };
+
+      services.prometheus.exporters.kea = {
+        enable = true;
+        controlSocketPaths = [
+          "http://127.0.0.1:8000"
+        ];
       };
     };
 
···
     client.wait_until_succeeds("ping -c 5 10.0.0.1")
     router.wait_until_succeeds("ping -c 5 10.0.0.3")
     nameserver.wait_until_succeeds("kdig +short client.lan.nixos.test @10.0.0.2 | grep -q 10.0.0.3")
+    router.log(router.execute("curl 127.0.0.1:9547")[1])
+    router.succeed("curl --no-buffer 127.0.0.1:9547 | grep -qE '^kea_dhcp4_addresses_assigned_total.*1.0$'")
   '';
 })

pkgs/servers/monitoring/prometheus/kea-exporter.nix

···
 { lib
 , python3Packages
 , fetchPypi
+, nixosTests
 }:
 
 python3Packages.buildPythonApplication rec {
···
     $out/bin/kea-exporter --help > /dev/null
     $out/bin/kea-exporter --version | grep -q ${version}
   '';
+
+  passthru.tests = {
+    inherit (nixosTests) kea;
+  };
 
   meta = with lib; {
     changelog = "https://github.com/mweinelt/kea-exporter/blob/v${version}/HISTORY";