🤖 Extract constant to ease testing

We're not concerned with where the cached file is for testing purposes;
so instead of hard-coding a value that can change in the ENV, let's
compare the constant that we use in the code.

tl;dr - Don't rely on magic strings

app/models/account.rb

@@ -111,14 +111,16 @@ def switch_host!(cname)
     Hyrax::Engine.routes.default_url_options[:host] = cname
   end
 
+  DEFAULT_FILE_CACHE_STORE = ENV.fetch('HYKU_CACHE_ROOT', '/app/samvera/file_cache')
+
   def setup_tenant_cache(is_enabled)
     Rails.application.config.action_controller.perform_caching = is_enabled
     ActionController::Base.perform_caching = is_enabled
     # rubocop:disable Style/ConditionalAssignment
     if is_enabled
       Rails.application.config.cache_store = :redis_cache_store, { url: Redis.current.id }
     else
-      Rails.application.config.cache_store = :file_store, ENV.fetch('HYKU_CACHE_ROOT', '/app/samvera/file_cache')
+      Rails.application.config.cache_store = :file_store, DEFAULT_FILE_CACHE_STORE
     end
     # rubocop:enable Style/ConditionalAssignment
     Rails.cache = ActiveSupport::Cache.lookup_store(Rails.application.config.cache_store)

spec/models/account_spec.rb

@@ -130,7 +130,7 @@
       it "reverts to using file store when cache is off" do
         account.settings[:cache_api] = false
         account.switch!
-        expect(Rails.application.config.cache_store).to eq([:file_store, kind_of(String)])
+        expect(Rails.application.config.cache_store).to eq([:file_store, described_class::DEFAULT_FILE_CACHE_STORE])
       end
     end
 
@@ -140,7 +140,7 @@
       it "uses the file store" do
         expect(Rails.application.config.action_controller.perform_caching).to be_falsey
         expect(ActionController::Base.perform_caching).to be_falsey
-        expect(Rails.application.config.cache_store).to eq([:file_store, kind_of(String)])
+        expect(Rails.application.config.cache_store).to eq([:file_store, described_class::DEFAULT_FILE_CACHE_STORE])
       end
     end