feat: scaffold plugin foundation

tests/Unit/ContainerTest.php

@@ -0,0 +1,45 @@
+<?php
+
+namespace WPContentSync\Tests\Unit;
+
+use PHPUnit\Framework\TestCase;
+use WPContentSync\Container;
+
+class ContainerTest extends TestCase {
+	public function test_it_returns_registered_service(): void {
+		$container = new Container();
+		$service   = new \stdClass();
+
+		$container->set( 'example', $service );
+
+		self::assertSame( $service, $container->get( 'example' ) );
+	}
+
+	public function test_it_reuses_factory_result(): void {
+		$container = new Container();
+		$calls     = 0;
+
+		$container->factory(
+			'example',
+			static function () use ( &$calls ): \stdClass {
+				++$calls;
+				return new \stdClass();
+			}
+		);
+
+		$first  = $container->get( 'example' );
+		$second = $container->get( 'example' );
+
+		self::assertSame( $first, $second );
+		self::assertSame( 1, $calls );
+	}
+
+	public function test_it_throws_for_unknown_service(): void {
+		$container = new Container();
+
+		$this->expectException( \InvalidArgumentException::class );
+		$this->expectExceptionMessage( 'Service "missing" is not registered.' );
+
+		$container->get( 'missing' );
+	}
+}