Magento 2 – Add Custom Block Below Cart Summary Page

Try like this,

<reference name="checkout.cart">

   <block type="test/test" before="coupon" name="custom-block"  template="test/cart_test.phtml" />

</reference>

call your custom block before coupon in app\design\frontend\package\theme\template\checkout\cart.phtml,

<?php echo $this->getChildHtml('custom-block'); ?>

 <?php echo $this->getChildHtml('coupon') ?>

First you need to add the following to your config.xml under the <config> tag:

<frontend>
    <layout>
        <updates>
            <expressdelivery>
                <file>expressdelivery.xml</file>
            </expressdelivery>
        </updates>
    </layout>
</frontend>

Then you need to create your layout file app/design/frontend/base/default/layout/expressdelivery.xml with the following content:

<?xml version="0.1.0">
<layout version="0.1.0">

    <checkout_cart_index>
         <reference name="checkout.cart">
              <block type="core/template" name="extra_block" template="link/to/your/template" />
         </reference>
    </checkout_cart_index>

</layout>

Then in your app/design/frontend/<your_package>/<your_theme>/template/checkout/cart.phtml you'll need to add the following code:

<?php echo $this->getChildHtml('extra_block'); ?>

Before this code:

<?php echo $this->getChildHtml('crosssell') ?>