diff --git a/specs/utils.spec.cjs b/specs/utils.spec.cjs
new file mode 100644
index 0000000..3636dd0
--- /dev/null
+++ b/specs/utils.spec.cjs
@@ -0,0 +1,40 @@
+const { describe, expect, it } = require("@jest/globals");
+const { processDate, removeHidden } = require("../lib/utils");
+
+describe("Utils", () => {
+	describe("removeHidden", () => {
+		it("should remove files that start with dot", () => {
+			const filesList = [
+				"a.png",
+				"b.png",
+				".DS_Store",
+				"not_the_droids_you_are_looking_for.txt",
+			];
+
+			expect(removeHidden(filesList)).toEqual([
+				"a.png",
+				"b.png",
+				"not_the_droids_you_are_looking_for.txt",
+			]);
+		});
+	});
+
+	describe("processDate", () => {
+		it("should throw Invalid date if args[0] is not a date", () => {
+			//@ts-expect-error
+			expect(() => processDate(5)).toThrow("Invalid date");
+			//@ts-expect-error
+			expect(() => processDate({})).toThrow("Invalid date");
+			//@ts-expect-error
+			expect(() => processDate("ciao")).toThrow("Invalid date");
+			//@ts-expect-error
+			expect(() => processDate(true)).toThrow("Invalid date");
+		});
+
+		it("should convert a Date object to a valid W3C date", () => {
+			expect(processDate(new Date(2020, 6, 1, 0, 0, 0, 0))).toBe(
+				"2020-07-01T00:00:00Z",
+			);
+		});
+	});
+});