test: cover formatJoinDate edge cases

test/FormatDate.ts

@@ -1,14 +1,30 @@
 import assert from "node:assert/strict";
+import { describe, it } from "node:test";
 import { formatJoinDate } from "../src/lib/format-date";
 
-const validIsoDate = "2026-07-27T12:00:00.000Z";
-const expectedDate = new Date(validIsoDate).toLocaleDateString(undefined, {
-  year: "numeric",
-  month: "long",
-  day: "numeric",
-});
+const expectedDate = (value: string) =>
+  new Date(value).toLocaleDateString(undefined, {
+    year: "numeric",
+    month: "long",
+    day: "numeric",
+  });
+
+describe("formatJoinDate", () => {
+  it("formats a valid ISO date", () => {
+    const value = "2026-07-27T12:00:00.000Z";
+    assert.equal(formatJoinDate(value), expectedDate(value));
+  });
 
-assert.equal(formatJoinDate(validIsoDate), expectedDate);
-assert.equal(formatJoinDate("not-a-date"), "not-a-date");
+  it("returns an invalid date unchanged", () => {
+    assert.equal(formatJoinDate("not-a-date"), "not-a-date");
+  });
 
-console.log("FormatDate tests passed.");
+  it("returns an empty string unchanged", () => {
+    assert.equal(formatJoinDate(""), "");
+  });
+
+  it("formats an ISO date with a timezone offset", () => {
+    const value = "2026-07-27T18:30:00+05:30";
+    assert.equal(formatJoinDate(value), expectedDate(value));
+  });
+});