feat(lib): add nix-unit tests for lib helpers

Cover the pure khanelinix helpers (base64 decode, module capitalize /
boolToNum / option builders / attr-priority helpers, file mergeAttrs,
and theme constructors) with nix-unit cases kept next to the library in
lib/tests.

Wire them through a flake-parts module, guarding the nix-unit import the
same way the git-hooks module is guarded, and route the tests output via
the dev partition so `nix-unit --flake .#tests` and the generated
checks.<system>.nix-unit both resolve.

Author: khaneliman

flake/default.nix

@@ -24,5 +24,6 @@ in
     "devShells"
     "formatter"
     "templates"
+    "tests"
   ] (_: "dev");
 }

flake/dev/default.nix

@@ -13,6 +13,7 @@ in
     ./checks.nix
     ./parse.nix
     ./templates.nix
+    ./tests.nix
     ./treefmt.nix
   ];
 

flake/dev/tests.nix

@@ -0,0 +1,30 @@
+{
+  inputs,
+  lib,
+  self,
+  ...
+}:
+let
+  hasNixUnit = inputs.nix-unit ? modules;
+in
+{
+  imports = lib.optional hasNixUnit inputs.nix-unit.modules.flake.default;
+
+  # Pure `lib.khanelinix` helper tests, run via `nix flake check` (check
+  # `nix-unit`) or ad hoc with `nix-unit --flake .#tests` from the dev shell.
+  # Cases live next to the library in `lib/tests`.
+  flake.tests = lib.mkIf hasNixUnit (import ../../lib/tests { inherit self lib; });
+
+  perSystem = _: {
+    nix-unit = lib.mkIf hasNixUnit {
+      # `checks.<system>.nix-unit` re-evaluates `self#tests` in the build
+      # sandbox. Pass the primary inputs to avoid refetching them, and allow
+      # network for the remaining transitive inputs this partitioned flake
+      # drags in through its overlays (e.g. home-manager).
+      inputs = {
+        inherit (inputs) nixpkgs flake-parts nix-unit;
+      };
+      allowNetwork = true;
+    };
+  };
+}

lib/tests/default.nix

@@ -0,0 +1,185 @@
+{
+  self,
+  lib,
+}:
+let
+  inherit (self.lib)
+    base64
+    file
+    module
+    theme
+    ;
+in
+{
+  # base64.decode
+  testBase64DecodeHello = {
+    expr = base64.decode "aGVsbG8=";
+    expected = "hello";
+  };
+
+  testBase64DecodeNoPadding = {
+    expr = base64.decode "Zm9vYmFy";
+    expected = "foobar";
+  };
+
+  testBase64DecodeOnePad = {
+    expr = base64.decode "Zm9vYmE=";
+    expected = "fooba";
+  };
+
+  testBase64DecodeTwoPad = {
+    expr = base64.decode "Zm9vYg==";
+    expected = "foob";
+  };
+
+  # module.capitalize
+  testCapitalizeWord = {
+    expr = module.capitalize "hello";
+    expected = "Hello";
+  };
+
+  testCapitalizeSingle = {
+    expr = module.capitalize "a";
+    expected = "A";
+  };
+
+  testCapitalizeEmpty = {
+    expr = module.capitalize "";
+    expected = "";
+  };
+
+  # module.boolToNum
+  testBoolToNumTrue = {
+    expr = module.boolToNum true;
+    expected = 1;
+  };
+
+  testBoolToNumFalse = {
+    expr = module.boolToNum false;
+    expected = 0;
+  };
+
+  # module.enabled / module.disabled
+  testEnabled = {
+    expr = module.enabled;
+    expected = {
+      enable = true;
+    };
+  };
+
+  testDisabled = {
+    expr = module.disabled;
+    expected = {
+      enable = false;
+    };
+  };
+
+  # module.enableForSystem keeps modules with no `systems` or a matching one.
+  testEnableForSystem = {
+    expr = module.enableForSystem "x86_64-linux" [
+      { name = "any"; }
+      {
+        name = "darwin-only";
+        systems = [ "aarch64-darwin" ];
+      }
+      {
+        name = "linux-only";
+        systems = [ "x86_64-linux" ];
+      }
+    ];
+    expected = [
+      { name = "any"; }
+      {
+        name = "linux-only";
+        systems = [ "x86_64-linux" ];
+      }
+    ];
+  };
+
+  # module.mkOpt / module.mkBoolOpt resolve to module-system options.
+  testMkOptDefault = {
+    expr = (module.mkOpt' lib.types.int 5).default;
+    expected = 5;
+  };
+
+  testMkBoolOptDefault = {
+    expr = (module.mkBoolOpt' true).default;
+    expected = true;
+  };
+
+  # module.default-attrs / module.force-attrs wrap values with merge priorities.
+  testDefaultAttrsContent = {
+    expr = (module.default-attrs { a = 1; }).a.content;
+    expected = 1;
+  };
+
+  testDefaultAttrsPriority = {
+    expr = (module.default-attrs { a = 1; }).a.priority;
+    expected = 1000;
+  };
+
+  testForceAttrsPriority = {
+    expr = (module.force-attrs { a = 1; }).a.priority;
+    expected = 50;
+  };
+
+  # file.mergeAttrs (later sets win)
+  testMergeAttrs = {
+    expr = file.mergeAttrs [
+      {
+        a = 1;
+        b = 1;
+      }
+      {
+        b = 2;
+        c = 3;
+      }
+    ];
+    expected = {
+      a = 1;
+      b = 2;
+      c = 3;
+    };
+  };
+
+  testMergeAttrsEmpty = {
+    expr = file.mergeAttrs [ ];
+    expected = { };
+  };
+
+  # theme helpers
+  testThemeMkColorScheme = {
+    expr = theme.mkColorScheme "test" { bg = "#000000"; };
+    expected = {
+      name = "test";
+      colors = {
+        bg = "#000000";
+      };
+      type = "colorScheme";
+    };
+  };
+
+  testThemeGetColors = {
+    expr = theme.getColors {
+      colors = {
+        fg = "#ffffff";
+      };
+    };
+    expected = {
+      fg = "#ffffff";
+    };
+  };
+
+  testThemeGetColorsMissing = {
+    expr = theme.getColors { };
+    expected = { };
+  };
+
+  testThemeVariants = {
+    expr = theme.variants;
+    expected = {
+      light = "light";
+      dark = "dark";
+    };
+  };
+}