added unit tests for result

src/result.test.ts

@@ -0,0 +1,45 @@
+import { describe, expect, test } from "bun:test";
+import { Err, Ok } from "./result.js";
+
+describe("result", () => {
+  test("Err", () => {
+    const result = Err(new Error("test error"));
+    expect(result.success).toBeFalse();
+    if (!result.success) {
+      expect(result.error.message).toBe("test error");
+    }
+
+    // @ts-expect-error
+    result.payload;
+  });
+
+  test("Err different type", () => {
+    const result = Err<string>("test error");
+    expect(result.success).toBeFalse();
+    if (!result.success) {
+      expect(result.error).toBe("test error");
+    }
+  });
+
+  test("Ok", () => {
+    const result = Ok();
+    expect(result.success).toBeTrue();
+    expect("payload" in result).toBeFalse();
+
+    // @ts-expect-error
+    result.payload;
+    // @ts-expect-error
+    result.error;
+  });
+
+  test("Ok payload", () => {
+    const result = Ok("test payload");
+    expect(result.success).toBeTrue();
+    if (result.success) {
+      expect(result.payload).toBe("test payload");
+    }
+
+    // @ts-expect-error
+    result.error;
+  });
+});

src/result.ts

@@ -9,7 +9,7 @@ export function Ok<
   P extends string | number | object | undefined = undefined,
   R = P extends undefined ? OkResult : OkResult<P>
 >(payload?: P): R {
-  if (payload === undefined) {
+  if (payload !== undefined) {
     return { success: true, payload } as R;
   }
   return { success: true } as R;