make flake.nix test pure

t/jobs/basic.nix

@@ -1,4 +1,6 @@
-with import ./config.nix;
+{ system ? builtins.currentSystem }:
+
+with import ./config.nix { inherit system; };
 {
   empty_dir =
     mkDerivation {

t/jobs/config.nix.in

@@ -1,9 +1,11 @@
+{ system ? builtins.currentSystem }:
+
 rec {
   path = "@testPath@";
 
   mkDerivation = args:
     derivation ({
-      system = builtins.currentSystem;
+      inherit system;
       PATH = path;
     } // args);
   mkContentAddressedDerivation = args: mkDerivation ({

t/jobs/flake-checks/flake.nix

@@ -1,6 +1,11 @@
 {
-  outputs = { ... }: {
-    checks =
-      import ./basic.nix;
-  };
+  outputs = { self, ... }:
+    let
+      systems = [ "x86_64-linux" "aarch64-linux" "x86_64-darwin" "aarch64-darwin" ];
+      forAllSystems = f: builtins.listToAttrs (map (system: { name = system; value = f system; }) systems);
+    in {
+      checks = forAllSystems (system:
+        import ./basic.nix { inherit system; }
+      );
+    };
 }

t/jobs/flake-hydraJobs/flake.nix

@@ -1,6 +1,11 @@
 {
-  outputs = { ... }: {
-    hydraJobs =
-      import ./basic.nix;
-  };
+  outputs = { self, ... }:
+    let
+      systems = [ "x86_64-linux" "aarch64-linux" "x86_64-darwin" "aarch64-darwin" ];
+      forAllSystems = f: builtins.listToAttrs (map (system: { name = system; value = f system; }) systems);
+    in {
+      hydraJobs = forAllSystems (system:
+        import ./basic.nix { inherit system; }
+      );
+    };
 }