test: add frontend test suite

src/favorites.test.ts

@@ -0,0 +1,27 @@
+import { describe, expect, it } from "vitest";
+import { isFavorite, readFavorites, toggleFavorite } from "./favorites";
+
+describe("favorites localStorage helpers", () => {
+  it("returns an empty list for missing, invalid, or non-array values", () => {
+    expect(readFavorites()).toEqual([]);
+
+    localStorage.setItem("ark_favorites", "not-json");
+    expect(readFavorites()).toEqual([]);
+
+    localStorage.setItem("ark_favorites", JSON.stringify({ id: "r1" }));
+    expect(readFavorites()).toEqual([]);
+  });
+
+  it("filters non-string entries and toggles favorite ids", () => {
+    localStorage.setItem("ark_favorites", JSON.stringify(["r1", 123, "r2"]));
+    expect(readFavorites()).toEqual(["r1", "r2"]);
+
+    expect(toggleFavorite("r3")).toBe(true);
+    expect(isFavorite("r3")).toBe(true);
+    expect(readFavorites()).toEqual(["r1", "r2", "r3"]);
+
+    expect(toggleFavorite("r1")).toBe(false);
+    expect(isFavorite("r1")).toBe(false);
+    expect(readFavorites()).toEqual(["r2", "r3"]);
+  });
+});