add nix-unit tests

tests/default.nix

@@ -0,0 +1,47 @@
+let
+  bootstrap = import ../nt/primitives/bootstrap;
+
+  nt = import ../nt {
+    mix = import ../nt/mix {
+      this = bootstrap;
+    };
+    # flake.nix passes `flake = inputs.self`
+    flake = builtins.getFlake ../.;
+  };
+
+  dummyTest = {
+    expr = 1;
+    expected = 1;
+  };
+in {
+  testPass = dummyTest;
+
+  testMaybe = let
+    maybe-mod = import ./maybe.nix {this = bootstrap;};
+
+    inherit
+      (maybe-mod)
+      Maybe
+      Some
+      None
+      ;
+  in {
+    expr = Some true;
+    expected = {
+      _''traps''_ = {
+        _'nt = {
+          derive = ["nt::&Maybe"];
+          instance = true;
+          ops = {
+            "nt::&Maybe" = {
+              unwrap = f: self: f self.${bootstrap.ntDynamicTrapdoorKey}.value;
+            };
+          };
+          req = {};
+          sig = "nt::Some";
+        };
+        _'ntDyn = {value = true;};
+      };
+    };
+  };
+}