nixos-test-driver: Make overridable

nixos/doc/manual/default.nix

@@ -64,6 +64,7 @@ let
       eval = nixos-lib.evalTest {
         # Avoid evaluating a NixOS config prototype.
         config.node.type = types.deferredModule;
+        config.hostPkgs = pkgs;
         options._module.args = mkOption { internal = true; };
       };
     in

nixos/doc/manual/redirects.json

@@ -211,6 +211,9 @@
   "test-opt-nodeDefaults": [
     "index.html#test-opt-nodeDefaults"
   ],
+  "test-opt-pythonTestDriverPackage": [
+    "index.html#test-opt-pythonTestDriverPackage"
+  ],
   "test-opt-rawTestDerivationArg": [
     "index.html#test-opt-rawTestDerivationArg"
   ],

nixos/lib/testing/driver.nix

@@ -9,15 +9,10 @@ let
 
   # Reifies and correctly wraps the python test driver for
   # the respective qemu version and with or without ocr support
-  testDriver = hostPkgs.python3Packages.callPackage ../test-driver {
+  testDriver = config.pythonTestDriverPackage.override {
     inherit (config) enableOCR extraPythonPackages;
     qemu_pkg = config.qemu.package;
-    imagemagick_light = hostPkgs.imagemagick_light.override { inherit (hostPkgs) libtiff; };
-    tesseract4 = hostPkgs.tesseract4.override { enableLanguages = [ "eng" ]; };
-
     enableNspawn = config.containers != { };
-    # We want `pkgs.systemd`, *not* `python3Packages.system`.
-    systemd = hostPkgs.systemd;
   };
 
   vlans = map (
@@ -135,6 +130,12 @@ let
 in
 {
   options = {
+    pythonTestDriverPackage = mkOption {
+      description = "Package containing the python NixOS test driver implemetnation";
+      type = types.package;
+      default = hostPkgs.nixos-test-driver;
+      readOnly = true;
+    };
 
     driver = mkOption {
       description = "Package containing a script that runs the test.";

pkgs/top-level/all-packages.nix

@@ -146,6 +146,14 @@ with pkgs;
 
   inherit (nix-update) nix-update-script;
 
+  nixos-test-driver = pkgs.python3Packages.callPackage ../../nixos/lib/test-driver {
+    qemu_pkg = pkgs.qemu;
+    imagemagick_light = pkgs.imagemagick_light.override { inherit (pkgs) libtiff; };
+    tesseract4 = pkgs.tesseract4.override { enableLanguages = [ "eng" ]; };
+    # We want `pkgs.systemd`, *not* `python3Packages.system`.
+    systemd = pkgs.systemd;
+  };
+
   ### Push NixOS tests inside the fixed point
 
   # See also allTestsForSystem in nixos/release.nix