Updated the test system

test/coalesce.test.js

@@ -0,0 +1,9 @@
+const expect = require('expect');
+const {coalesce} = require('./_30s.js');
+
+test('coalesce is a Function', () => {
+  expect(coalesce).toBeInstanceOf(Function);
+});
+test('Returns the first non-null/undefined argument', () => {
+  expect(coalesce(null, undefined, '', NaN, 'Waldo')).toEqual('');
+});