rails-test-cache: Add post

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+#+TITLE: Testing Rails Components That Require Cache
+#+DATE: 2023-04-28T00:14:14-04:00
+#+DRAFT: false
+#+DESCRIPTION: How to test rails components that require cache without caching everything
+#+TAGS[]: ruby rails cache
+#+KEYWORDS[]: ruby rails cache
+#+SLUG:
+#+SUMMARY:
+
+If you're in the default testing environment your rails cache is
+=ActiveSupport::Cache::NullStore= which will always succeed but it
+doesn't actually store or return anything.
+
+There's an almost completely undocumented function called
+=with_local_cache= that gets implemented on =NullStore= that lets
+you run a block with a =MemoryStore= instead of a =NullStore=. This
+happens because it =prepends= the
+=ActiveSupport::Cache::Strategy::LocalCache= class.
+
+#+begin_src ruby
+   Rails.cache.class.name
+   # => "ActiveSupport::Cache::NullStore"
+   Rails.cache.write("a", 3)
+   # => true
+   Rails.cache.read("a")
+   # => nil
+   Rails.cache.with_local_cache do
+     Rails.cache.write("a", 5)
+     p Rails.cache.read("a")
+   end
+   5
+   # => 5
+#+end_src