nixosTests.docker-tools: add bulk-layer test

A regression test for https://github.com/NixOS/nixpkgs/issues/78744.

nixos/tests/docker-tools.nix

@@ -83,5 +83,11 @@ import ./make-test.nix ({ pkgs, ... }: {
 
       # Ensure image with only 2 layers can be loaded
       $docker->succeed("docker load --input='${pkgs.dockerTools.examples.two-layered-image}'");
+
+      # Ensure the bulk layer didn't miss store paths
+      # Regression test for https://github.com/NixOS/nixpkgs/issues/78744
+      $docker->succeed("docker load --input='${pkgs.dockerTools.examples.bulk-layer}'");
+      # This ensure the two output paths (ls and hello) are in the layer
+      $docker->succeed("docker run bulk-layer ls /bin/hello");
     '';
 })