Make it pass a minimal test

nixos/modules/services/monitoring/prometheus/alertmanager.nix

@@ -137,44 +137,40 @@ let
         '';
       };
     };
-    mkAMConfig = amCfg: amVersion:
-      config = mkMerge [
-        (mkIf amCfg.enable {
-          assertions = singleton {
-            assertion = amCfg.configuration != null || amCfg.configText != null;
-            message = "Can not enable alertmanager without a configuration. "
-             + "Set either the `configuration` or `configText` attribute.";
-          };
-        })
-        (mkIf amCfg.enable {
-          networking.firewall.allowedTCPPorts = optional amCfg.openFirewall amCfg.port;
+    mkAMConfig = amCfg: amVersion: [
+      (mkIf amCfg.enable {
+        assertions = singleton {
+          assertion = amCfg.configuration != null || amCfg.configText != null;
+          message = "Can not enable alertmanager without a configuration. "
+           + "Set either the `configuration` or `configText` attribute.";
+        };
+      })
+      (mkIf amCfg.enable {
+        networking.firewall.allowedTCPPorts = optional amCfg.openFirewall amCfg.port;
 
-          systemd.services."alertmanager${amVersion}" = {
-            wantedBy = [ "multi-user.target" ];
-            after    = [ "network.target" ];
-            script = ''
-              ${amCfg.package}/bin/alertmanager \
-                ${concatStringsSep " \\\n  " cmdlineArgs}
-            '';
-            serviceConfig = {
-              User = amCfg.user;
-              Group = amCfg.group;
-              Restart  = "always";
-              PrivateTmp = true;
-              WorkingDirectory = "/tmp";
-              ExecReload = "${pkgs.coreutils}/bin/kill -HUP $MAINPID";
-            };
+        systemd.services."alertmanager${amVersion}" = {
+          wantedBy = [ "multi-user.target" ];
+          after    = [ "network.target" ];
+          script = ''
+            ${amCfg.package}/bin/alertmanager \
+              ${concatStringsSep " \\\n  " cmdlineArgs}
+          '';
+          serviceConfig = {
+            User = amCfg.user;
+            Group = amCfg.group;
+            Restart  = "always";
+            PrivateTmp = true;
+            WorkingDirectory = "/tmp";
+            ExecReload = "${pkgs.coreutils}/bin/kill -HUP $MAINPID";
           };
-        })
-      ];
+        };
+      })
+    ];
 in {
   options = {
     services.prometheus.alertmanager = amOptions;
     services.prometheus2.alertmanager = amOptions;
   };
 
-  config = mkMerge [
-    (mkAMConfig cfg "")
-    (mkAMConfig cfg2 "2")
-  ];
+  config = mkMerge ((mkAMConfig cfg "") ++ (mkAMConfig cfg2 "2"));
 }

nixos/modules/services/monitoring/prometheus/default.nix

@@ -22,8 +22,10 @@ let
 
   # a wrapper that verifies that the configuration is valid for
   # prometheus 2
-  prom2toolCheck = what: name: file: pkgs.runCommand "${name}-${what}-checked"
-    { buildInputs = [ cfg2.package ]; } ''
+  prom2toolCheck = what: name: file:
+    pkgs.runCommand
+      "${name}-${replaceStrings [" "] [""] what}-checked"
+      { buildInputs = [ cfg2.package ]; } ''
     ln -s ${file} $out
     promtool ${what} $out
   '';
@@ -64,7 +66,7 @@ let
   # This becomes the main config file for Prometheus 2
   promConfig2 = {
     global = cfg2.globalConfig;
-    rule_files = map (prom2toolCheck "check-rules" "rules") (cfg2.ruleFiles ++ [
+    rule_files = map (prom2toolCheck "check rules" "rules") (cfg2.ruleFiles ++ [
       (pkgs.writeText "prometheus.rules" (concatStringsSep "\n" cfg2.rules))
     ]);
     scrape_configs = cfg2.scrapeConfigs;
@@ -83,7 +85,7 @@ let
     yml = if cfg2.configText != null then
       pkgs.writeText "prometheus.yml" cfg2.configText
       else generatedPrometheus2Yml;
-    in promtoo2lCheck "check-config" "prometheus.yml" yml;
+    in prom2toolCheck "check config" "prometheus.yml" yml;
 
   cmdlineArgs2 = cfg2.extraFlags ++ [
     "--storage.tsdb.path=${cfg2.dataDir}/data/"
@@ -704,7 +706,7 @@ in {
         after    = [ "network.target" ];
         script = ''
           #!/bin/sh
-          exec ${cfg.package}/bin/prometheus \
+          exec ${cfg2.package}/bin/prometheus \
             ${concatStringsSep " \\\n  " cmdlineArgs2}
         '';
         serviceConfig = {

nixos/tests/prometheus-2.nix

@@ -0,0 +1,34 @@
+import ./make-test.nix {
+  name = "prometheus-2";
+
+  nodes = {
+    one = { pkgs, ... }: {
+      services.prometheus2 = {
+        enable = true;
+        scrapeConfigs = [{
+          job_name = "prometheus";
+          static_configs = [{
+            targets = [ "127.0.0.1:9090" ];
+            labels = { instance = "localhost"; };
+          }];
+        }];
+        rules = [
+          ''
+            groups:
+              - name: test
+                rules:
+                  - record: testrule
+                    expr: count(up{job="prometheus"})
+          ''
+        ];
+      };
+    };
+  };
+
+  testScript = ''
+    startAll;
+    $one->waitForUnit("prometheus2.service");
+    $one->waitForOpenPort(9090);
+    $one->succeed("curl -s http://127.0.0.1:9090/metrics");
+  '';
+}