Quality of life improvements all around.

tests/AppTest.php

@@ -0,0 +1,28 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Tests;
+
+use PHPUnit\Framework\TestCase;
+use PHPUnit\Framework\Attributes\CoversClass;
+use Psr\Log\LoggerInterface;
+use App\App;
+
+#[CoversClass(App::class)]
+final class AppTest extends \PHPUnit\Framework\TestCase
+{
+    public function testNonexistentConfigFile(): void
+    {
+        $this->expectException(\Exception::class);
+        new App('no_file');
+        $this->fail('Exception was not thrown');
+    }
+
+    public function testGoodConfig(): void
+    {
+        $app = new App('config.example.yml');
+        $this->assertEquals('output.log', $app->getConfig('log'));
+        $this->assertInstanceOf(LoggerInterface::class, $app->getLogger());
+    }
+}