Revert "nixosTests: Resolve alias kgx = gnome-console"

This reverts commit a486968a6e.

nixos/lib/testing/nodes.nix

@@ -1,7 +1,18 @@
 testModuleArgs@{ config, lib, hostPkgs, nodes, ... }:
 
 let
-  inherit (lib) mkOption mkForce optional types mapAttrs mkDefault mdDoc;
+  inherit (lib)
+    literalExpression
+    literalMD
+    mapAttrs
+    mdDoc
+    mkDefault
+    mkIf
+    mkOption mkForce
+    optional
+    optionalAttrs
+    types
+    ;
 
   baseOS =
     import ../eval-config.nix {
@@ -16,7 +27,8 @@ let
             {
               virtualisation.qemu.package = testModuleArgs.config.qemu.package;
             })
-          ({
+          (optionalAttrs (!config.node.pkgsReadOnly) {
+            key = "nodes.nix-pkgs";
             config = {
               # Ensure we do not use aliases. Ideally this is only set
               # when the test framework is used by Nixpkgs NixOS tests.
@@ -71,6 +83,30 @@ in
       default = { };
     };
 
+    node.pkgs = mkOption {
+      description = mdDoc ''
+        The Nixpkgs to use for the nodes.
+
+        Setting this will make the `nixpkgs.*` options read-only, to avoid mistakenly testing with a Nixpkgs configuration that diverges from regular use.
+      '';
+      type = types.nullOr types.pkgs;
+      default = null;
+      defaultText = literalMD ''
+        `null`, so construct `pkgs` according to the `nixpkgs.*` options as usual.
+      '';
+    };
+
+    node.pkgsReadOnly = mkOption {
+      description = mdDoc ''
+        Whether to make the `nixpkgs.*` options read-only. This is only relevant when [`node.pkgs`](#test-opt-node.pkgs) is set.
+
+        Set this to `false` when any of the [`nodes`](#test-opt-nodes) needs to configure any of the `nixpkgs.*` options. This will slow down evaluation of your test a bit.
+      '';
+      type = types.bool;
+      default = config.node.pkgs != null;
+      defaultText = literalExpression ''node.pkgs != null'';
+    };
+
     node.specialArgs = mkOption {
       type = types.lazyAttrsOf types.raw;
       default = { };
@@ -103,5 +139,11 @@ in
         config.nodes;
 
     passthru.nodes = config.nodesCompat;
+
+    defaults = mkIf config.node.pkgsReadOnly {
+      nixpkgs.pkgs = config.node.pkgs;
+      imports = [ ../../modules/misc/nixpkgs/read-only.nix ];
+    };
+
   };
 }

nixos/tests/all-tests.nix

@@ -46,7 +46,7 @@ let
   inherit
     (rec {
       doRunTest = arg: ((import ../lib/testing-python.nix { inherit system pkgs; }).evalTest {
-        imports = [ arg ];
+        imports = [ arg readOnlyPkgs ];
       }).config.result;
       findTests = tree:
         if tree?recurseForDerivations && tree.recurseForDerivations
@@ -65,6 +65,23 @@ let
     runTestOn
     ;
 
+  # Using a single instance of nixpkgs makes test evaluation faster.
+  # To make sure we don't accidentally depend on a modified pkgs, we make the
+  # related options read-only. We need to test the right configuration.
+  #
+  # If your service depends on a nixpkgs setting, first try to avoid that, but
+  # otherwise, you can remove the readOnlyPkgs import and test your service as
+  # usual.
+  readOnlyPkgs =
+    # TODO: We currently accept this for nixosTests, so that the `pkgs` argument
+    #       is consistent with `pkgs` in `pkgs.nixosTests`. Can we reinitialize
+    #       it with `allowAliases = false`?
+    # warnIf pkgs.config.allowAliases "nixosTests: pkgs includes aliases."
+    {
+      _class = "nixosTest";
+      node.pkgs = pkgs;
+    };
+
 in {
 
   # Testing the test driver
@@ -77,7 +94,7 @@ in {
 
   _3proxy = runTest ./3proxy.nix;
   aaaaxy = runTest ./aaaaxy.nix;
-  acme = runTest ./acme.nix;
+  acme = runTest { imports = [ ./acme.nix ]; };
   adguardhome = runTest ./adguardhome.nix;
   aesmd = runTestOn ["x86_64-linux"] ./aesmd.nix;
   agate = runTest ./web-servers/agate.nix;