clanLib: init flakeModules for better testing

lib/test/default.nix

@@ -6,6 +6,9 @@ let
     ;
 in
 {
+  flakeModules = clanLib.callLib ./flakeModules.nix { };
+
+  #
   minifyModule = ./minify.nix;
   sopsModule = ./sops.nix;
   # A function that returns an extension to runTest

lib/test/flakeModules.nix

@@ -0,0 +1,56 @@
+{ lib, clanLib }:
+{
+
+  /**
+    This function is used to create a module that can be imported into flake-parts
+    and used to run eval tests.
+
+    Usage: `lib.modules.importApply makeEvalChecks { module = module-under-test; testArgs = { }; }`
+
+    returns a module to be imported into flake-parts
+
+    Which in turn adds to the flake:
+
+    - legacyPackages.<system>.eval-tests-<testName>: The attribute set passed to nix-unit. (Exposed for debugging i.e. via nix repl).
+    - checks.<system>.eval-tests-<testName>: A derivation that can be built and fails if nix-unit fails
+  */
+  makeEvalChecks =
+    {
+      self,
+      inputs,
+      testName,
+      tests,
+      module,
+      testArgs ? { },
+    }:
+    let
+      inputOverrides = builtins.concatStringsSep " " (
+        builtins.map (input: " --override-input ${input} ${inputs.${input}}") (builtins.attrNames inputs)
+      );
+      attrName = "eval-tests-${testName}";
+    in
+    {
+      pkgs,
+      system,
+      ...
+    }:
+    {
+      legacyPackages.${attrName} = import tests (
+        {
+          inherit clanLib lib module;
+        }
+        // testArgs
+      );
+      checks.${attrName} = pkgs.runCommand "tests" { nativeBuildInputs = [ pkgs.nix-unit ]; } ''
+        export HOME="$(realpath .)"
+
+        nix-unit --eval-store "$HOME" \
+          --extra-experimental-features flakes \
+          --show-trace \
+          ${inputOverrides} \
+          --flake ${self}#legacyPackages.${system}.${attrName}
+        touch $out
+      '';
+
+    };
+}