Updated the test system

test/gcd.test.js

@@ -0,0 +1,12 @@
+const expect = require('expect');
+const {gcd} = require('./_30s.js');
+
+test('gcd is a Function', () => {
+  expect(gcd).toBeInstanceOf(Function);
+});
+test('Calculates the greatest common divisor between two or more numbers/arrays', () => {
+  expect(gcd(8, 36)).toBe(4);
+});
+test('Calculates the greatest common divisor between two or more numbers/arrays', () => {
+  expect(gcd(...[12, 8, 32])).toEqual(4);
+});