nixos/testing: Embrace callTest

My conception of its input was wrong. It is quite a useful construct,
even if its name is a bit weird.

nixos/lib/testing-python.nix

@@ -26,7 +26,6 @@ rec {
   extraTestModule = {
     config = {
       hostPkgs = pkgs;
-      minimalResult = hydra;
     };
   };
 

nixos/lib/testing/run.nix

@@ -16,22 +16,22 @@ in
       '';
     };
 
-    run = mkOption {
+    test = mkOption {
       type = types.package;
       description = ''
-        Derivation that runs the test.
+        Derivation that runs the test as its "build" process.
       '';
     };
   };
 
   config = {
-    run = hostPkgs.stdenv.mkDerivation {
+    test = lib.lazyDerivation { # lazyDerivation improves performance when only passthru items and/or meta are used.
+      derivation = hostPkgs.stdenv.mkDerivation {
         name = "vm-test-run-${config.name}";
 
         requiredSystemFeatures = [ "kvm" "nixos-test" ];
 
-      buildCommand =
-        ''
+        buildCommand = ''
           mkdir -p $out
 
           # effectively mute the XMLLogger
@@ -44,6 +44,8 @@ in
 
         meta = config.meta;
       };
+      inherit (config) passthru meta;
+    };
 
     # useful for inspection (debugging / exploration)
     passthru.config = config;

nixos/release.nix

@@ -22,8 +22,8 @@ let
     import ./tests/all-tests.nix {
       inherit system;
       pkgs = import ./.. { inherit system; };
-      callTest = t: {
-        ${system} = hydraJob t.test;
+      callTest = config: {
+        ${system} = hydraJob config.test;
       };
     } // {
       # for typechecking of the scripts and evaluation of
@@ -32,8 +32,8 @@ let
         import ./tests/all-tests.nix {
         inherit system;
         pkgs = import ./.. { inherit system; };
-        callTest = t: {
-          ${system} = hydraJob t.test.driver;
+        callTest = config: {
+          ${system} = hydraJob config.driver;
         };
       };
     };

nixos/tests/all-tests.nix

@@ -1,4 +1,11 @@
-{ system, pkgs, callTest }:
+{ system,
+  pkgs,
+
+  # Projects the test configuration into a the desired value; usually
+  # the test runner: `config: config.test`.
+  callTest,
+
+}:
 # The return value of this function will be an attrset with arbitrary depth and
 # the `anything` returned by callTest at its test leafs.
 # The tests not supported by `system` will be replaced with `{}`, so that
@@ -29,11 +36,17 @@ let
 
   inherit
     (rec {
-      doRunTest = (import ../lib/testing-python.nix { inherit system pkgs; }).runTest;
+      doRunTest = arg: (import ../lib/testing-python.nix { inherit system pkgs; }).runTest {
+        imports = [ arg { inherit callTest; } ];
+      };
       findTests = tree:
         if tree?recurseForDerivations && tree.recurseForDerivations
-        then mapAttrs (k: findTests) (builtins.removeAttrs tree ["recurseForDerivations"])
-        else callTest ({ test = tree; });
+        then
+          mapAttrs
+            (k: findTests)
+            (builtins.removeAttrs tree ["recurseForDerivations"])
+        else callTest tree;
+
       runTest = arg: let r = doRunTest arg; in findTests r;
       runTestOn = systems: arg:
         if elem system systems then runTest arg

pkgs/top-level/all-packages.nix

@@ -140,14 +140,14 @@ with pkgs;
   nixosTests = import ../../nixos/tests/all-tests.nix {
     inherit pkgs;
     system = stdenv.hostPlatform.system;
-    callTest = t: t.test;
+    callTest = config: config.test;
   } // {
     # for typechecking of the scripts and evaluation of
     # the nodes, without running VMs.
     allDrivers = import ../../nixos/tests/all-tests.nix {
       inherit pkgs;
       system = stdenv.hostPlatform.system;
-      callTest = t: t.test.driver;
+      callTest = config: config.test.driver;
     };
   };