Refactor file_download_link Kernel tests

Here's a patch that refactors the kernel tests AND adds a tiny bit of new test coverage that ends up exposing a bug! Yay! The new test cases are token-less cases for when the token module is enabled. That's where the bug creeps in. Having a data provider makes adding cases soooo much easier.

Ah, darnit. My patch included the fix:

+++ b/src/Plugin/Field/FieldFormatter/FileDownloadLink.php
@@ -327,8 +328,9 @@ class FileDownloadLink extends FileFormatterBase implements ContainerFactoryPlug
-        // Next line is important. See https://www.drupal.org/node/2528662.
-        $bubbleable_metadata->applyTo($elements[$delta]);
+        // Apply cacheability of tokens to render array.
+        $bubbleable_metadata->merge(CacheableMetadata::createFromRenderArray($elements[$delta]))
+          ->applyTo($elements[$delta]);

I was previously overwriting the existing cacheable metadata rather than adding to it. Now it's fixed.

Automatically closed - issue fixed for 2 weeks with no activity.