Safer handling of backend date formats

and add frontend testing

frontend/src/components/Table/Formatter/DateFormatter.test.tsx

@@ -0,0 +1,77 @@
+import { DateTimeFormat } from "src/locale";
+import { afterAll, beforeAll, describe, expect, it } from "vitest";
+
+describe("DateFormatter", () => {
+	// Keep a reference to the real Intl to restore later
+	const RealIntl = global.Intl;
+	const desiredTimeZone = "Europe/London";
+	const desiredLocale = "en-GB";
+
+	beforeAll(() => {
+		// Ensure Node-based libs using TZ behave deterministically
+		try {
+			process.env.TZ = desiredTimeZone;
+		} catch {
+			// ignore if not available
+		}
+
+		// Mock Intl.DateTimeFormat so formatting is stable regardless of host
+		const MockedDateTimeFormat = class extends RealIntl.DateTimeFormat {
+			constructor(
+				_locales?: string | string[],
+				options?: Intl.DateTimeFormatOptions,
+			) {
+				super(desiredLocale, {
+					...options,
+					timeZone: desiredTimeZone,
+				});
+			}
+		} as unknown as typeof Intl.DateTimeFormat;
+
+		global.Intl = {
+			...RealIntl,
+			DateTimeFormat: MockedDateTimeFormat,
+		};
+	});
+
+	afterAll(() => {
+		// Restore original Intl after tests
+		global.Intl = RealIntl;
+	});
+
+	it("format date from iso date", () => {
+		const value = "2024-01-01T00:00:00.000Z";
+		const text = DateTimeFormat(value);
+		expect(text).toBe("Monday, 01/01/2024, 12:00:00 am");
+	});
+
+	it("format date from unix timestamp number", () => {
+		const value = 1762476112;
+		const text = DateTimeFormat(value);
+		expect(text).toBe("Friday, 07/11/2025, 12:41:52 am");
+	});
+
+	it("format date from unix timestamp string", () => {
+		const value = "1762476112";
+		const text = DateTimeFormat(value);
+		expect(text).toBe("Friday, 07/11/2025, 12:41:52 am");
+	});
+
+	it("catch bad format from string", () => {
+		const value = "this is not a good date";
+		const text = DateTimeFormat(value);
+		expect(text).toBe("this is not a good date");
+	});
+
+	it("catch bad format from number", () => {
+		const value = -100;
+		const text = DateTimeFormat(value);
+		expect(text).toBe("-100");
+	});
+
+	it("catch bad format from number as string", () => {
+		const value = "-100";
+		const text = DateTimeFormat(value);
+		expect(text).toBe("-100");
+	});
+});