Updated the test system

test/decapitalize.test.js

@@ -0,0 +1,12 @@
+const expect = require('expect');
+const {decapitalize} = require('./_30s.js');
+
+test('decapitalize is a Function', () => {
+  expect(decapitalize).toBeInstanceOf(Function);
+});
+test('Works with default parameter', () => {
+  expect(decapitalize('FooBar')).toBe('fooBar');
+});
+test('Works with second parameter set to true', () => {
+  expect(decapitalize('FooBar', true)).toBe('fOOBAR');
+});