Test switching to a new config and deactivating.

test/nix/modules/default.nix

@@ -4,7 +4,42 @@
 }:
 
 lib.flip lib.mapAttrs' system-manager.lib.images.ubuntu.${system} (imgName: image:
-lib.nameValuePair "example-${imgName}"
+let
+  newConfig = system-manager.lib.makeSystemConfig {
+    modules = [
+      ({ lib, pkgs, ... }: {
+        config = {
+          nixpkgs.hostPlatform = "x86_64-linux";
+
+          services.nginx.enable = true;
+
+          environment.etc = {
+            foo_new = {
+              text = ''
+                This is just a test!
+              '';
+            };
+          };
+          systemd.services.new-service = {
+            enable = true;
+            description = "new-service";
+            serviceConfig = {
+              Type = "oneshot";
+              RemainAfterExit = true;
+              ExecReload = "${lib.getBin pkgs.coreutils}/bin/true";
+            };
+            wantedBy = [ "system-manager.target" ];
+            script = ''
+              sleep 2
+            '';
+          };
+        };
+      })
+    ];
+  };
+in
+lib.nameValuePair
+  "example-${imgName}"
   (system-manager.lib.make-vm-test {
     inherit system;
     modules = [
@@ -37,9 +72,21 @@ lib.nameValuePair "example-${imgName}"
 
             node1.wait_for_unit("service-9.service")
             node1.wait_for_file("/etc/baz/bar/foo2")
+            node1.wait_for_file("/etc/a/nested/example/foo3")
             node1.wait_for_file("/etc/foo.conf")
             node1.succeed("grep -F 'launch_the_rockets = true' /etc/foo.conf")
             node1.fail("grep -F 'launch_the_rockets = false' /etc/foo.conf")
+
+            node1.execute("${newConfig}/bin/activate")
+            node1.wait_for_unit("new-service.service")
+            node1.wait_until_fails("systemctl status service-9.service")
+            node1.wait_until_fails("cat /etc/a/nested/example/foo3")
+            node1.wait_until_fails("cat /etc/baz/bar/foo2")
+            node1.wait_for_file("/etc/foo_new")
+
+            node1.execute("${newConfig}/bin/deactivate")
+            node1.wait_until_fails("systemctl status new-service.service")
+            node1.wait_until_fails("cat /etc/foo_new")
           '';
         })
     ];