Override code-behind for a block in Magento

I am writing a module to extend the Core/Catalog/Product/View/Media.php class so I can expose new methods in my template. I followed a number of guides online, including Alan Storms excellent series, but have had little success. ( http://alanstorm.com/magento_config )

I posted my code on Github: https://github.com/razialx/Magento-Overwrite-Block

I am not getting any errors in the logs, it just isn't loading my class. Very perplexed.

One thought I had was that I may only be able to rewrite classes that are explicitly defined. I know the Mage_Catalog_Block_Product_View_Media class is never defined in a config file, though I assume it is referenced by the layout xml file catalog.xml

<block type="catalog/product_view_media" name="product.info.media" as="media" template="catalog/product/view/media.phtml"/>

Solution

Your config.xml is slightly off. Give the following a try.

 <config>
    <modules>
        <Test_Catalog>
            <version>1.0.0.0.0</version>
        </Test_Catalog>
    </modules>
    <global>
        <blocks>
            <catalog>
                <rewrite>
                    <product_view_media>Test_Catalog_Block_Product_View_Media</product_view_media>
                </rewrite>
            </catalog>
        </blocks>
    </global>
</config>

Your <blocks> node needs to be enclosed in a <global> node.