services.prometheus.exporters.fastly: add a smoke test

nixos/modules/services/monitoring/prometheus/exporters/fastly.nix

@@ -33,7 +33,7 @@ in
       ${optionalString (cfg.tokenPath != null)
       "export FASTLY_API_TOKEN=$(cat ${toString cfg.tokenPath})"}
       ${pkgs.prometheus-fastly-exporter}/bin/fastly-exporter \
-        -endpoint http://${cfg.listenAddress}:${toString cfg.port}/metrics
+        -listen http://${cfg.listenAddress}:${toString cfg.port}
         ${optionalString cfg.debug "-debug true"} \
         ${optionalString (cfg.configFile != null) "-config-file ${cfg.configFile}"}
     '';

nixos/tests/prometheus-exporters.nix

@@ -259,6 +259,19 @@ let
       '';
     };
 
+    fastly = {
+      exporterConfig = {
+        enable = true;
+        tokenPath = pkgs.writeText "token" "abc123";
+      };
+
+      # noop: fastly's exporter can't start without first talking to fastly
+      # see: https://github.com/peterbourgon/fastly-exporter/issues/87
+      exporterTest = ''
+        succeed("true");
+      '';
+    };
+
     fritzbox = {
       # TODO add proper test case
       exporterConfig = {