Add unit tests for dateFormatter

Author: wojtekmaj

packages/react-date-picker/src/shared/dateFormatter.spec.ts

@@ -0,0 +1,23 @@
+import { describe, expect, it } from 'vitest';
+
+import { formatMonth, formatShortMonth } from './dateFormatter.js';
+
+describe('formatMonth', () => {
+  it('returns proper month name', () => {
+    const date = new Date(2017, 1, 1);
+
+    const formattedDate = formatMonth('en-US', date);
+
+    expect(formattedDate).toBe('February');
+  });
+});
+
+describe('formatShortMonth', () => {
+  it('returns proper short month name', () => {
+    const date = new Date(2017, 1, 1);
+
+    const formattedDate = formatShortMonth('en-US', date);
+
+    expect(formattedDate).toBe('Feb');
+  });
+});