anchor.diff:      smokeping = {
         exporterConfig = {
           enable = true;
  -        hosts = ["127.0.0.1"];
  +        hosts = [ "127.0.0.1" ];
         };
         exporterTest = ''
           wait_for_unit("prometheus-smokeping-exporter.service")
  
positive.code:                 syslog = {
                    listen_address = "udp://127.0.0.1:10000";
                    format = "rfc3164";
                    tags = ["nginx"];
                  };
                };
              }
  
negative.code:       };
        metricProvider = {
          # Mock rtl_433 binary to return a dummy metric stream.
          nixpkgs.overlays = [
            (self: super: {
              rtl_433 = self.runCommand "rtl_433" { } ''
                mkdir -p "$out/bin"
                cat <<EOF > "$out/bin/rtl_433"
                #!/bin/sh
                while true; do
                  printf '{"time" : "2020-04-26 13:37:42", "model" : "zopieux", "id" : 55, "channel" : 3, "temperature_C" : 18.000}\n'
                  sleep 4
                done
                EOF
                chmod +x "$out/bin/rtl_433"
              '';
            })
          ];
        };
        exporterTest = ''
          wait_for_unit("prometheus-rtl_433-exporter.service")
  