add vm test that runs in CI

.github/workflows/test.yml

@@ -10,4 +10,10 @@ jobs:
     - uses: cachix/install-nix-action@v22
       with:
         github_access_token: ${{ secrets.GITHUB_TOKEN }}
+        extra_nix_config: "system-features = nixos-test benchmark big-parallel kvm"
+    - uses: cachix/cachix-action@v12
+      with:
+        name: selfhostblocks
+        authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
     - run: nix flake check
+    - run: nix build .#checks.x86_64-linux.vms.postgresql

flake.nix

@@ -59,6 +59,10 @@
                   ./test/modules/postgresql.nix
                 ]);
             };
+
+            vms = {
+              postgresql = pkgs.callPackage ./test/vm/postgresql.nix {};
+            };
           };
       }
   );

test/vm/postgresql.nix

@@ -0,0 +1,14 @@
+{ pkgs, lib, ... }:
+let
+
+in pkgs.nixosTest {
+  name = "postgresql";
+
+  nodes.machine = { config, pkgs, ... }: {
+
+  };
+
+  testScript = { nodes, ... }: ''
+  start_all()
+  '';
+}