skopeo: add testNixFromDockerHub to passthru.tests

pkgs/development/tools/skopeo/default.nix

@@ -10,6 +10,7 @@
 , installShellFiles
 , makeWrapper
 , fuse-overlayfs
+, dockerTools
 }:
 
 buildGoModule rec {
@@ -53,6 +54,10 @@ buildGoModule rec {
     runHook postInstall
   '';
 
+  passthru.tests = {
+    inherit (dockerTools.examples) testNixFromDockerHub;
+  };
+
   meta = with lib; {
     description = "A command line utility for various operations on container images and image repositories";
     homepage = "https://github.com/containers/skopeo";