test(web): add unit tests for pure helper functions (#2454)

* test(web): add unit tests for pure helper functions

Add vitest configuration and tests for:
- relativeTime: time formatting (just now, minutes, hours, days, months, years)
- lastPageFromLink: GitHub Link header pagination parsing

These are the first tests for the web frontend. The test framework
(vitest) was already in package.json but had no config or test files.

* test(web): exercise real GitHub helpers

---------

Co-authored-by: Hu Qiantao <huqiantao@HudeMacBook-Air.local>
Co-authored-by: Hunter B <hmbown@gmail.com>

web/lib/github.test.ts

@@ -0,0 +1,78 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
+import { lastPageFromLink, relativeTime } from "./github";
+
+describe("relativeTime", () => {
+  beforeEach(() => {
+    vi.useFakeTimers();
+    vi.setSystemTime(new Date("2026-06-01T12:00:00Z"));
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  it("returns 'just now' for less than 30 seconds ago", () => {
+    expect(relativeTime("2026-06-01T11:59:45Z")).toBe("just now");
+  });
+
+  it("returns minutes for < 1 hour", () => {
+    expect(relativeTime("2026-06-01T11:55:00Z")).toBe("5m");
+    expect(relativeTime("2026-06-01T11:30:00Z")).toBe("30m");
+  });
+
+  it("returns hours for < 1 day", () => {
+    expect(relativeTime("2026-06-01T09:00:00Z")).toBe("3h");
+    expect(relativeTime("2026-05-31T18:00:00Z")).toBe("18h");
+  });
+
+  it("returns days before the 30-day month boundary", () => {
+    expect(relativeTime("2026-05-25T12:00:00Z")).toBe("7d");
+    expect(relativeTime("2026-05-03T12:00:00Z")).toBe("29d");
+  });
+
+  it("returns months for < 12 months", () => {
+    expect(relativeTime("2026-05-02T12:00:00Z")).toBe("1mo");
+    expect(relativeTime("2026-03-01T12:00:00Z")).toBe("3mo");
+    expect(relativeTime("2025-08-01T12:00:00Z")).toBe("10mo");
+  });
+
+  it("returns years for >= 12 months", () => {
+    expect(relativeTime("2024-06-01T12:00:00Z")).toBe("2y");
+    expect(relativeTime("2025-01-01T00:00:00Z")).toBe("1y");
+  });
+});
+
+describe("lastPageFromLink", () => {
+  it("returns undefined for null input", () => {
+    expect(lastPageFromLink(null)).toBeUndefined();
+  });
+
+  it("returns undefined for empty string", () => {
+    expect(lastPageFromLink("")).toBeUndefined();
+  });
+
+  it("extracts page from Link header with last rel", () => {
+    const link =
+      '<https://api.github.com/repos/Hmbown/CodeWhale/issues?page=5>; rel="last"';
+    expect(lastPageFromLink(link)).toBe(5);
+  });
+
+  it("extracts page from multi-part Link header", () => {
+    const link = [
+      '<https://api.github.com/repos/Hmbown/CodeWhale/issues?page=1>; rel="prev"',
+      '<https://api.github.com/repos/Hmbown/CodeWhale/issues?page=3>; rel="last"',
+    ].join(", ");
+    expect(lastPageFromLink(link)).toBe(3);
+  });
+
+  it("returns undefined when no last rel present", () => {
+    const link =
+      '<https://api.github.com/repos/Hmbown/CodeWhale/issues?page=1>; rel="prev"';
+    expect(lastPageFromLink(link)).toBeUndefined();
+  });
+
+  it("returns undefined for invalid URL format", () => {
+    const link = "not-a-valid-link-header; rel=last";
+    expect(lastPageFromLink(link)).toBeUndefined();
+  });
+});

web/lib/github.ts

@@ -70,7 +70,7 @@ async function contributorCount(res: Response): Promise<number> {
   return MIN_KNOWN_CONTRIBUTORS;
 }
 
-function lastPageFromLink(link: string | null): number | undefined {
+export function lastPageFromLink(link: string | null): number | undefined {
   if (!link) return undefined;
 
   for (const part of link.split(",")) {

web/package.json

@@ -8,6 +8,7 @@
     "prebuild": "node scripts/derive-facts.mjs",
     "build": "next build",
     "start": "next start",
+    "test": "vitest run",
     "lint": "eslint .",
     "preview": "opennextjs-cloudflare preview",
     "predeploy": "node scripts/check-kv-id.mjs",
@@ -31,9 +32,10 @@
     "postcss": "^8.5.14",
     "tailwindcss": "^3.4.17",
     "typescript": "^5.7.3",
+    "vitest": "^4.1.7",
     "wrangler": "^4.86.0"
   },
   "overrides": {
-    "postcss": "$postcss"
+    "postcss": "^8.5.14"
   }
 }

web/vitest.config.ts

@@ -0,0 +1,7 @@
+import { defineConfig } from "vitest/config";
+
+export default defineConfig({
+  test: {
+    include: ["lib/**/*.test.ts", "components/**/*.test.tsx"],
+  },
+});