diff --git a/src/engine/types.test.ts b/src/engine/types.test.ts
new file mode 100644
index 0000000..69dff10
--- /dev/null
+++ b/src/engine/types.test.ts
@@ -0,0 +1,41 @@
+import { describe, it, expect } from "vitest";
+import { qty, pct, Decimal } from "./types";
+
+describe("types", () => {
+  describe("qty", () => {
+    it("creates a quantity with default arguments", () => {
+      const result = qty(42);
+      expect(result.kind).toBe("quantity");
+      expect(result.value).toBeInstanceOf(Decimal);
+      expect(result.value.toNumber()).toBe(42);
+      expect(result.unit).toBeNull();
+      expect(result.repr).toBe("decimal");
+    });
+
+    it("creates a quantity with all arguments provided", () => {
+      const mockUnit = { id: "meter", dimension: "length", ratio: new Decimal(1), format: "m" } as any;
+      const result = qty("3.14", mockUnit, "hex");
+      expect(result.kind).toBe("quantity");
+      expect(result.value).toBeInstanceOf(Decimal);
+      expect(result.value.toString()).toBe("3.14");
+      expect(result.unit).toBe(mockUnit);
+      expect(result.repr).toBe("hex");
+    });
+  });
+
+  describe("pct", () => {
+    it("creates a percent value from number", () => {
+      const result = pct(25);
+      expect(result.kind).toBe("percent");
+      expect(result.value).toBeInstanceOf(Decimal);
+      expect(result.value.toNumber()).toBe(25);
+    });
+
+    it("creates a percent value from string", () => {
+      const result = pct("12.5");
+      expect(result.kind).toBe("percent");
+      expect(result.value).toBeInstanceOf(Decimal);
+      expect(result.value.toString()).toBe("12.5");
+    });
+  });
+});