add PHP boilerplate

tests/unit/HelloWorldTest.php

@@ -0,0 +1,19 @@
+<?php
+declare(strict_types=1);
+
+namespace Tests\Unit;
+
+use NoteCat\HelloWorld;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * @covers NoteCat\HelloWorld
+ */
+final class HelloWorldTest extends TestCase
+{
+    public function testGetHello(): void
+    {
+        $hello = new HelloWorld();
+        $this->assertSame('Hello Drone! :3', $hello->getHello());
+    }
+}