Updated the test system

test/isSymbol.test.js

@@ -0,0 +1,9 @@
+const expect = require('expect');
+const {isSymbol} = require('./_30s.js');
+
+test('isSymbol is a Function', () => {
+  expect(isSymbol).toBeInstanceOf(Function);
+});
+test('Checks if the given argument is a symbol', () => {
+  expect(isSymbol(Symbol('x'))).toBeTruthy();
+});