admin_footer action hook not working for me?

I created and activated a plugin with the following code:

add_action('admin_footer', 'test_function');
function test_function(){
	echo "WE ARE HERE";
}

However I’m not able to get this to work. I don’t see this when I’m in wp-admin. When I open wp-admin/admin-footer.php, I do see the call to “do_action(‘admin_footer’, ”);” present, yet it doesn’t seem to be working. I have to manually add a call to test_function() in admin-footer.php to get the function to run.

Am I doing something wrong? Is there an additional step I’m missing?