Add cart test without checkout button for full branch coverage

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/js/cart.test.js

@@ -232,6 +232,26 @@ describe('initCart', () => {
         expect(document.getElementById('cart-count').textContent).toBe('1')
     })
 
+    it('works without checkout button', () => {
+        document.body.innerHTML = `
+            <div id="billetterie">
+                <div data-cart-item data-billet-id="1" data-price="10" data-max="5">
+                    <button data-cart-minus></button>
+                    <input data-cart-qty type="number" min="0" max="5" value="0" readonly>
+                    <button data-cart-plus></button>
+                    <span data-cart-line-total></span>
+                </div>
+                <span id="cart-total"></span><span id="cart-count"></span>
+            </div>
+        `
+        initCart()
+
+        document.querySelector('[data-cart-plus]').click()
+
+        expect(document.getElementById('cart-total').textContent).toBe('10,00 \u20AC')
+        expect(document.getElementById('cart-count').textContent).toBe('1')
+    })
+
     it('does not post when cart is empty on checkout', () => {
         const fetchMock = vi.fn()
         globalThis.fetch = fetchMock