Updated the test system

test/countOccurrences.test.js

@@ -0,0 +1,9 @@
+const expect = require('expect');
+const {countOccurrences} = require('./_30s.js');
+
+test('countOccurrences is a Function', () => {
+  expect(countOccurrences).toBeInstanceOf(Function);
+});
+test('Counts the occurrences of a value in an array', () => {
+  expect(countOccurrences([1, 1, 2, 1, 2, 3], 1)).toEqual(3);
+});