feat: add HasCart trait and ShareCartWithInertia

tests/Unit/Concerns/ShareCartWithInertiaTest.php

@@ -0,0 +1,54 @@
+<?php
+
+use Wearepixel\Cart\Cart;
+use Wearepixel\Cart\Concerns\ShareCartWithInertia;
+use Wearepixel\Cart\Drivers\SessionDriver;
+use Wearepixel\Cart\Tests\Helpers\SessionMock;
+
+function makeCartForInertia(): Cart
+{
+    $events = Mockery::mock('Illuminate\Contracts\Events\Dispatcher');
+    $events->shouldReceive('dispatch');
+
+    return new Cart(
+        new SessionDriver(new SessionMock, 'TESTKEY'),
+        $events,
+        'cart',
+        require __DIR__ . '/../../Helpers/ConfigMock.php',
+    );
+}
+
+beforeEach(function () {
+    $this->cart = makeCartForInertia();
+});
+
+afterEach(fn() => Mockery::close());
+
+describe('ShareCartWithInertia', function () {
+    test('data() returns items, total, subtotal, and count', function () {
+        $this->cart->add(1, 'Widget', 50.00, 2);
+
+        $data = ShareCartWithInertia::data($this->cart);
+
+        expect($data)->toHaveKeys(['items', 'total', 'subtotal', 'count']);
+        expect($data['count'])->toBe(2);
+        expect($data['subtotal'])->toBe(100.00);
+        expect($data['total'])->toBe(100.00);
+    });
+
+    test('data() returns empty state when cart is empty', function () {
+        $data = ShareCartWithInertia::data($this->cart);
+
+        expect($data['items'])->toBeEmpty();
+        expect($data['count'])->toBe(0);
+    });
+
+    test('data() items are plain arrays suitable for JSON serialization', function () {
+        $this->cart->add(1, 'Widget', 50.00, 1);
+
+        $data = ShareCartWithInertia::data($this->cart);
+
+        expect($data['items'])->toBeArray();
+        expect(json_encode($data))->toBeString();
+    });
+});