Added setExpirationDate implementation along with tests

src/processDate.ts

@@ -0,0 +1,17 @@
+import { dateToW3CString } from "./utils";
+import formatMessage, { ERROR, DEBUG } from "./messages";
+
+export function processDate(key: string, date: Date): string | null {
+	if (!(date instanceof Date)) {
+		return null;
+	}
+
+	const dateParse = dateToW3CString(date);
+
+	if (!dateParse) {
+		console.warn(formatMessage(DEBUG.DATE_FORMAT_UNMATCH, key));
+		return null;
+	}
+
+	return dateParse;
+}