Migrate mapper unit tests

tests/Unit/Mapper/CountMapperTest.php

@@ -0,0 +1,17 @@
+<?php
+/**
+ * @author Daniel J. Summers <daniel@bitbadger.solutions>
+ * @license MIT
+ */
+
+declare(strict_types=1);
+
+use BitBadger\PDODocument\Mapper\CountMapper;
+
+pest()->group('unit');
+
+describe('->map()', function () {
+    test('returns item 0 in the given array', function () {
+        expect((new CountMapper())->map([5, 8, 10]))->toBe(5);
+    });
+});