feat: switch from flake-parts & devenv to rensa + add nixtest

tests/lib_test.nix

@@ -0,0 +1,47 @@
+{
+  pkgs,
+  ntlib,
+  nixlet-lib,
+  ...
+}: {
+  suites."Lib Tests" = {
+    pos = __curPos;
+    tests = let
+      nixlet = nixlet-lib.mkNixlet ./fixtures/example;
+    in [
+      {
+        name = "mkNixlet fail on nonexistant nixlet.nix";
+        expected = {
+          success = false;
+          value = false;
+        };
+        actual = builtins.tryEval (nixlet-lib.mkNixlet "/nonexistant").name;
+      }
+      {
+        name = "mkNixlet success";
+        expected = {
+          name = "example";
+          version = "0.0.1";
+          description = "hello world";
+        };
+        actual = {inherit (nixlet) name description version;};
+      }
+      {
+        name = "Nixlet mkDocs";
+        type = "script";
+        script = let
+          docs = nixlet.mkDocs {};
+        in
+          # sh
+          ''
+            ${ntlib.helpers.path [pkgs.gnugrep]}
+            ${ntlib.helpers.scriptHelpers}
+            assert "-f ${docs}" "generated the file"
+            assert_file_contains "${docs}" '`example`'
+            assert_file_contains "${docs}" "Some description."
+            assert_file_contains "${docs}" '"Hello world!"'
+          '';
+      }
+    ];
+  };
+}