Add a test for chroot stores

tests/nixos/chroot-store.nix

@@ -0,0 +1,31 @@
+{ lib, config, nixpkgs, ... }:
+
+let
+  pkgs = config.nodes.machine.nixpkgs.pkgs;
+  pkgA = pkgs.hello;
+  pkgB = pkgs.cowsay;
+in {
+  name = "chroot-store";
+
+  nodes =
+    { machine =
+        { config, lib, pkgs, ... }:
+        { virtualisation.writableStore = true;
+          virtualisation.additionalPaths = [ pkgA ];
+          environment.systemPackages = [ pkgB ];
+          nix.extraOptions = "experimental-features = nix-command";
+        };
+    };
+
+  testScript = { nodes }: ''
+    # fmt: off
+    start_all()
+
+    machine.succeed("nix copy --no-check-sigs --to /tmp/nix ${pkgA}")
+
+    machine.succeed("nix shell --store /tmp/nix ${pkgA} --command hello >&2")
+
+    # Test that /nix/store is available via an overlayfs mount.
+    machine.succeed("nix shell --store /tmp/nix ${pkgA} --command cowsay foo >&2")
+  '';
+}

tests/nixos/default.nix

@@ -161,4 +161,6 @@ in
   cgroups = runNixOSTestFor "x86_64-linux" ./cgroups;
 
   fetchurl = runNixOSTestFor "x86_64-linux" ./fetchurl.nix;
+
+  chrootStore = runNixOSTestFor "x86_64-linux" ./chroot-store.nix;
 }