Add release Nix expression

release.nix

@@ -10,6 +10,6 @@ let
 in
 {
   tests = import ./tests {
-    inherit pkgs system nix-processmgmt processManagers profiles;
+    inherit nixpkgs system nix-processmgmt processManagers profiles;
   };
 }

tests/default.nix

@@ -1,4 +1,4 @@
-{ pkgs ? import <nixpkgs> { inherit system; }
+{ nixpkgs ? <nixpkgs>
 , system ? builtins.currentSystem
 , processManagers ? [ "supervisord" "sysvinit" "systemd" "docker" "disnix" "s6-rc" ]
 , profiles ? [ "privileged" "unprivileged" ]
@@ -6,8 +6,10 @@
 }:
 
 let
+  pkgs = import nixpkgs { inherit system; };
+
   testService = import "${nix-processmgmt}/nixproc/test-driver/universal.nix" {
-    inherit system;
+    inherit nixpkgs system;
   };
 in
 {

tests/docker/default.nix

@@ -19,7 +19,8 @@ testService {
       )
     '';
 
-  inherit processManagers;
+  # It is useless to run Docker in Docker
+  processManagers = builtins.filter (processManager: processManager != "docker") processManagers;
 
   # There's an experimental rootless feature for Docker, but a hassle to setup. As a result, we disable unprivileged mode
   profiles = builtins.filter (profile: profile == "privileged") profiles;