Add PHPUnit test suite, PSR-4 refactor, lint+test CI jobs (v1.3.1)

- 57 unit tests covering ProductType, StockManager, CartHandler, Plugin,
  Admin/ProductData, Admin/Settings using Brain Monkey + Mockery
- WooCommerce class stubs for testing without WP installation
- PHP lint and test jobs in release workflow (test gate blocks release)
- PSR-4 namespace change: WC_Composable_Product -> Magdev\WcComposableProduct
- PascalCase filenames for all classes under includes/

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/Unit/CartHandlerTest.php

@@ -0,0 +1,184 @@
+<?php
+/**
+ * CartHandler Tests
+ *
+ * @package Magdev\WcComposableProduct\Tests
+ */
+
+namespace Magdev\WcComposableProduct\Tests\Unit;
+
+use Magdev\WcComposableProduct\Tests\TestCase;
+use Magdev\WcComposableProduct\CartHandler;
+use Brain\Monkey\Functions;
+use Brain\Monkey\Actions;
+use Brain\Monkey\Filters;
+
+class CartHandlerTest extends TestCase
+{
+    protected function setUp(): void
+    {
+        parent::setUp();
+
+        // Clean up POST superglobal between tests
+        $_POST = [];
+    }
+
+    protected function tearDown(): void
+    {
+        $_POST = [];
+        parent::tearDown();
+    }
+
+    public function testConstructor_RegistersExpectedHooks(): void
+    {
+        $handler = new CartHandler();
+
+        self::assertNotFalse(has_filter('woocommerce_add_to_cart_validation', 'Magdev\WcComposableProduct\CartHandler->validate_add_to_cart()'));
+        self::assertNotFalse(has_filter('woocommerce_add_cart_item_data', 'Magdev\WcComposableProduct\CartHandler->add_cart_item_data()'));
+        self::assertNotFalse(has_filter('woocommerce_get_cart_item_from_session', 'Magdev\WcComposableProduct\CartHandler->get_cart_item_from_session()'));
+        self::assertNotFalse(has_filter('woocommerce_get_item_data', 'Magdev\WcComposableProduct\CartHandler->display_cart_item_data()'));
+        self::assertNotFalse(has_action('woocommerce_before_calculate_totals', 'Magdev\WcComposableProduct\CartHandler->calculate_cart_item_price()'));
+        self::assertNotFalse(has_action('woocommerce_single_product_summary', 'Magdev\WcComposableProduct\CartHandler->render_product_selector()'));
+        self::assertNotFalse(has_filter('woocommerce_is_purchasable', 'Magdev\WcComposableProduct\CartHandler->hide_default_add_to_cart()'));
+    }
+
+    public function testHideDefaultAddToCart_ReturnsFalseForComposable(): void
+    {
+        $handler = new CartHandler();
+        $product = $this->createProductMock(['get_type' => 'composable']);
+
+        $result = $handler->hide_default_add_to_cart(true, $product);
+        $this->assertFalse($result);
+    }
+
+    public function testHideDefaultAddToCart_PassesThroughForSimple(): void
+    {
+        $handler = new CartHandler();
+        $product = $this->createProductMock(['get_type' => 'simple']);
+
+        $result = $handler->hide_default_add_to_cart(true, $product);
+        $this->assertTrue($result);
+    }
+
+    public function testValidateAddToCart_PassesThroughForNonComposable(): void
+    {
+        $product = $this->createProductMock(['get_type' => 'simple']);
+        Functions\expect('wc_get_product')->with(1)->andReturn($product);
+
+        $handler = new CartHandler();
+        $result = $handler->validate_add_to_cart(true, 1, 1);
+
+        $this->assertTrue($result);
+    }
+
+    public function testValidateAddToCart_ReturnsFalseWhenNoProductsSelected(): void
+    {
+        $product = $this->createProductMock(['get_type' => 'composable']);
+        Functions\expect('wc_get_product')->with(1)->andReturn($product);
+        Functions\expect('wc_add_notice')->once();
+
+        $_POST['composable_products'] = [];
+
+        $handler = new CartHandler();
+        $result = $handler->validate_add_to_cart(true, 1, 1);
+
+        $this->assertFalse($result);
+    }
+
+    public function testValidateAddToCart_ReturnsFalseWhenNoPostData(): void
+    {
+        $product = $this->createProductMock(['get_type' => 'composable']);
+        Functions\expect('wc_get_product')->with(1)->andReturn($product);
+        Functions\expect('wc_add_notice')->once();
+
+        // No $_POST['composable_products'] at all
+        $handler = new CartHandler();
+        $result = $handler->validate_add_to_cart(true, 1, 1);
+
+        $this->assertFalse($result);
+    }
+
+    public function testAddCartItemData_AddsSelectionsForComposable(): void
+    {
+        $product = $this->createProductMock(['get_type' => 'composable']);
+        Functions\expect('wc_get_product')->with(1)->andReturn($product);
+        Functions\expect('absint')->andReturnUsing(function ($val) {
+            return abs((int) $val);
+        });
+
+        $_POST['composable_products'] = ['101', '102'];
+
+        $handler = new CartHandler();
+        $result = $handler->add_cart_item_data([], 1);
+
+        $this->assertArrayHasKey('composable_products', $result);
+        $this->assertSame([101, 102], $result['composable_products']);
+        $this->assertArrayHasKey('unique_key', $result);
+    }
+
+    public function testAddCartItemData_PassesThroughForNonComposable(): void
+    {
+        $product = $this->createProductMock(['get_type' => 'simple']);
+        Functions\expect('wc_get_product')->with(1)->andReturn($product);
+
+        $handler = new CartHandler();
+        $result = $handler->add_cart_item_data(['existing' => 'data'], 1);
+
+        $this->assertSame(['existing' => 'data'], $result);
+    }
+
+    public function testGetCartItemFromSession_RestoresComposableProducts(): void
+    {
+        $handler = new CartHandler();
+        $result = $handler->get_cart_item_from_session(
+            ['data' => 'test'],
+            ['composable_products' => [101, 102]]
+        );
+
+        $this->assertSame([101, 102], $result['composable_products']);
+    }
+
+    public function testGetCartItemFromSession_PassesThroughWithoutComposableData(): void
+    {
+        $handler = new CartHandler();
+        $result = $handler->get_cart_item_from_session(
+            ['data' => 'test'],
+            []
+        );
+
+        $this->assertArrayNotHasKey('composable_products', $result);
+    }
+
+    public function testDisplayCartItemData_FormatsProductNames(): void
+    {
+        $mock1 = $this->createProductMock(['get_name' => 'Product A']);
+        $mock2 = $this->createProductMock(['get_name' => 'Product B']);
+
+        Functions\expect('wc_get_product')
+            ->andReturnUsing(function ($id) use ($mock1, $mock2) {
+                return match ($id) {
+                    101 => $mock1,
+                    102 => $mock2,
+                    default => false,
+                };
+            });
+
+        $handler = new CartHandler();
+        $result = $handler->display_cart_item_data(
+            [],
+            ['composable_products' => [101, 102]]
+        );
+
+        $this->assertCount(1, $result);
+        $this->assertStringContainsString('Product A', $result[0]['value']);
+        $this->assertStringContainsString('Product B', $result[0]['value']);
+    }
+
+    public function testDisplayCartItemData_ReturnsEmptyForNonComposable(): void
+    {
+        $handler = new CartHandler();
+        $result = $handler->display_cart_item_data([], []);
+
+        $this->assertSame([], $result);
+    }
+}