test(promos): add unit tests for isPromoDateActive date range logic

Make today injectable via optional parameter for deterministic testing.

src/assets/data/promos/types.test.ts

@@ -0,0 +1,81 @@
+import { describe, expect, test } from "bun:test";
+import { isPromoDateActive } from "./types";
+import type { PromoData } from "./types";
+
+const makePromo = (overrides: Partial<PromoData> = {}): PromoData => ({
+  type: "banner",
+  message: "Test promo",
+  ...overrides,
+});
+
+describe("isPromoDateActive", () => {
+  describe("no date range set", () => {
+    test("returns true when neither startDate nor endDate is set", () => {
+      expect(isPromoDateActive(makePromo(), "2026-04-28")).toBe(true);
+    });
+  });
+
+  describe("startDate only", () => {
+    test("returns false before startDate", () => {
+      expect(
+        isPromoDateActive(makePromo({ startDate: "2026-04-29" }), "2026-04-28"),
+      ).toBe(false);
+    });
+
+    test("returns true on startDate", () => {
+      expect(
+        isPromoDateActive(makePromo({ startDate: "2026-04-29" }), "2026-04-29"),
+      ).toBe(true);
+    });
+
+    test("returns true after startDate", () => {
+      expect(
+        isPromoDateActive(makePromo({ startDate: "2026-04-29" }), "2026-05-01"),
+      ).toBe(true);
+    });
+  });
+
+  describe("endDate only", () => {
+    test("returns true before endDate", () => {
+      expect(
+        isPromoDateActive(makePromo({ endDate: "2026-05-13" }), "2026-05-12"),
+      ).toBe(true);
+    });
+
+    test("returns true on endDate", () => {
+      expect(
+        isPromoDateActive(makePromo({ endDate: "2026-05-13" }), "2026-05-13"),
+      ).toBe(true);
+    });
+
+    test("returns false after endDate", () => {
+      expect(
+        isPromoDateActive(makePromo({ endDate: "2026-05-13" }), "2026-05-14"),
+      ).toBe(false);
+    });
+  });
+
+  describe("startDate and endDate", () => {
+    const promo = makePromo({ startDate: "2026-04-29", endDate: "2026-05-13" });
+
+    test("returns false before window", () => {
+      expect(isPromoDateActive(promo, "2026-04-28")).toBe(false);
+    });
+
+    test("returns true on first day", () => {
+      expect(isPromoDateActive(promo, "2026-04-29")).toBe(true);
+    });
+
+    test("returns true mid-window", () => {
+      expect(isPromoDateActive(promo, "2026-05-06")).toBe(true);
+    });
+
+    test("returns true on last day", () => {
+      expect(isPromoDateActive(promo, "2026-05-13")).toBe(true);
+    });
+
+    test("returns false after window", () => {
+      expect(isPromoDateActive(promo, "2026-05-14")).toBe(false);
+    });
+  });
+});

src/assets/data/promos/types.ts

@@ -66,8 +66,10 @@ const routeMatchesAllowlist = (path: string, allowlist: string[]) =>
   allowlist.some((route) => path === route || path.startsWith(`${route}/`));
 
 /** Returns false if today is outside the promo's startDate/endDate window. */
-export const isPromoDateActive = (promo: PromoData): boolean => {
-  const today = new Date().toISOString().slice(0, 10);
+export const isPromoDateActive = (
+  promo: PromoData,
+  today = new Date().toISOString().slice(0, 10),
+): boolean => {
   if (promo.startDate && today < promo.startDate) return false;
   if (promo.endDate && today > promo.endDate) return false;
   return true;