Updated the test system

test/pluralize.test.js

@@ -0,0 +1,26 @@
+const expect = require('expect');
+const {pluralize} = require('./_30s.js');
+
+test('pluralize is a Function', () => {
+  expect(pluralize).toBeInstanceOf(Function);
+});
+test('Produces the plural of the word', () => {
+  expect(pluralize(0, 'apple')).toBe('apples');
+});
+test('Produces the singular of the word', () => {
+  expect(pluralize(1, 'apple')).toBe('apple');
+});
+test('Produces the plural of the word', () => {
+  expect(pluralize(2, 'apple')).toBe('apples');
+});
+test('Prodices the defined plural of the word', () => {
+  expect(pluralize(2, 'person', 'people')).toBe('people');
+});
+const PLURALS = {
+  person: 'people',
+  radius: 'radii'
+};
+const autoPluralize = pluralize(PLURALS);
+test('Works with a dictionary', () => {
+  expect(autoPluralize(2, 'person')).toBe('people');
+});