chore: import upstream snapshot with attribution

tests/unit/gamification/sharing.test.ts

@@ -0,0 +1,44 @@
+import { describe, it } from "node:test";
+import assert from "node:assert/strict";
+import { transferTokens, getBalance, getHistory } from "../../../src/lib/gamification/sharing";
+
+describe("Token Sharing", () => {
+  describe("transferTokens", () => {
+    it("rejects self-transfer", async () => {
+      const result = await transferTokens("user1", "user1", 100);
+      assert.equal(result.success, false);
+      assert.ok(result.error?.includes("yourself"));
+    });
+
+    it("rejects zero amount", async () => {
+      const result = await transferTokens("user1", "user2", 0);
+      assert.equal(result.success, false);
+    });
+
+    it("rejects negative amount", async () => {
+      const result = await transferTokens("user1", "user2", -100);
+      assert.equal(result.success, false);
+    });
+
+    it("returns idempotency key on success", async () => {
+      // This will fail due to insufficient balance, but validates the flow
+      const result = await transferTokens("user1", "user2", 100);
+      // Either succeeds or fails with balance error — idempotencyKey should be a string
+      assert.equal(typeof result.idempotencyKey, "string");
+    });
+  });
+
+  describe("getBalance", () => {
+    it("returns number", async () => {
+      const balance = await getBalance("test-user");
+      assert.equal(typeof balance, "number");
+    });
+  });
+
+  describe("getHistory", () => {
+    it("returns array", async () => {
+      const history = await getHistory("test-user");
+      assert.ok(Array.isArray(history));
+    });
+  });
+});