anchor.diff:        exporterConfig = {
           enable = true;
           group = "openvpn";
  -        statusPaths = ["/run/openvpn-test"];
  -      };
  -      metricProvider = {
  -        users.groups.openvpn = {};
  +        statusPaths = [ "/run/openvpn-test" ];
  +      };
  +      metricProvider = {
  +        users.groups.openvpn = { };
           services.openvpn.servers.test = {
             config = ''
               dev tun
  
positive.code: { system ? builtins.currentSystem
  , config ? {}
  , pkgs ? import ../.. { inherit system config; }
  }:
  
  let
    inherit (import ../lib/testing-python.nix { inherit system pkgs; }) makeTest;
    inherit (pkgs.lib) concatStringsSep maintainers mapAttrs mkMerge
                       removeSuffix replaceChars singleton splitString;
  
  /*
   * The attrset `exporterTests` contains one attribute
   * for each exporter test. Each of these attributes
   * is expected to be an attrset containing:
   *
   *  `exporterConfig`:
   *    this attribute set contains config for the exporter itself
   *
   *  `exporterTest`
   *    this attribute set contains test instructions
   *
   *  `metricProvider` (optional)
   *    this attribute contains additional machine config
   *
   *  `nodeName` (optional)
   *    override an incompatible testnode name
   *
   *  Example:
   *    exporterTests.<exporterName> = {
   *      exporterConfig = {
   *        enable = true;
   *      };
   *      metricProvider = {
   *        services.<metricProvider>.enable = true;
   *      };
   *      exporterTest = ''
   *        wait_for_unit("prometheus-<exporterName>-exporter.service")
   *        wait_for_open_port("1234")
   *        succeed("curl -sSf 'localhost:1234/metrics'")
   *      '';
   *    };
   *
   *  # this would generate the following test config:
   *
   *    nodes.<exporterName> = {
   *      services.prometheus.<exporterName> = {
   *        enable = true;
   *      };
   *      services.<metricProvider>.enable = true;
   *    };
   *
   *    testScript = ''
   *      <exporterName>.start()
   *      <exporterName>.wait_for_unit("prometheus-<exporterName>-exporter.service")
   *      <exporterName>.wait_for_open_port("1234")
   *      <exporterName>.succeed("curl -sSf 'localhost:1234/metrics'")
   *      <exporterName>.shutdown()
   *    '';
   */
  
    exporterTests = {
       apcupsd = {
        exporterConfig = {
          enable = true;
        };
  
negative.code:                 syslog = {
                    listen_address = "udp://127.0.0.1:10000";
                    format = "rfc3164";
                    tags = [ "nginx" ];
                  };
                };
              }
  