nixosTests.docker-tools: add bulk-layer test

A regression test for NixOS/nixpkgs#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");
     '';
 })

pkgs/build-support/docker/examples.nix

@@ -247,4 +247,15 @@ rec {
     maxLayers = 2;
   };
 
+  # 16. Create a layered image with more packages than max layers.
+  # coreutils and hello are part of the same layer
+  bulk-layer = pkgs.dockerTools.buildLayeredImage {
+    name = "bulk-layer";
+    tag = "latest";
+    contents = with pkgs; [
+      coreutils hello
+    ];
+    maxLayers = 2;
+  };
+
 }