nginx-pipeline: add basic test

tests/nginx-pipeline/default.nix

@@ -0,0 +1,39 @@
+{ nixpkgs, lib, matrix-lib, writeText, ... }:
+let
+  nixosConfig = nixpkgs.lib.nixosSystem {
+    system = "x86_64-linux";
+    modules = [
+      ../../module.nix
+      {
+        system.stateVersion = "23.11";
+        boot.isContainer = true;
+        services.matrix-synapse-next = {
+          enable = true;
+          enableNginx = true;
+
+          workers = {
+            enableMetrics = true;
+
+            federationSenders = 3;
+            federationReceivers = 3;
+            initialSyncers = 1;
+            normalSyncers = 1;
+            eventPersisters = 1;
+            useUserDirectoryWorker = true;
+          };
+
+          settings.server_name = "example.com";
+        };
+      }
+    ];
+  };
+
+  inherit (nixosConfig.config.services.matrix-synapse-next.workers) instances;
+in
+  writeText "matrix-synapse-next-nginx-pipeline-test.txt" ''
+    ${(lib.generators.toPretty {}) instances}
+
+    ====================================================
+
+    ${(lib.generators.toPretty {}) (matrix-lib.mapWorkersToUpstreamsByType instances)}
+  ''