Dynamic pricing, cart totals in PHPUnit

I am writing a plugin that lets users add a tip on the cart page. I use two filters to do so: woocommerce_add_cart_item & woocommerce_add_cart_item. Both use the same callback:

    public function setTipPrice($cart_item_data)
    {
        if ($cart_item_data['product_id'] == App::tipId() && array_key_exists('tip_size', $cart_item_data)) {
            $cart_item_data['data']->set_price($cart_item_data['tip_size']);
        }

        return $cart_item_data;
    }

This works as expected in the browser, but fails in PHPUnit. Is there something I have to call explicitly to fix this? The price of the tip is always 0.

Here’s the test:

    //  This test fails, but works in the browser.

    /** @test */
    public function it_can_have_a_custom_price_when_adding_to_the_cart()
    {
        App::install(); // creates the tip product
        
        WC()->cart->add_to_cart(App::tipId(), 1, 0, [], ['tip_size' => 10.00]);

        $this->assertEquals(10.00, WC()->cart->get_total_ex_tax());
    }

Any pointers?