Convert hash keys to strings #293 (#302)

* Convert hash keys to strings #293

Rails automatically converts keys to symbols, but this is not
standard behavior of the YAML parser, so we had a mismatch
here.

* Fix mixup #293

I wanted to revert my temporary changes to test data and
accidentally reverted the adjusted test for the previous
commit. This commit resolves that mixup.

---------

Co-authored-by: Martin Alfke <tuxmea@users.noreply.github.com>

app/models/hiera_data/hierarchy.rb

@@ -99,7 +99,7 @@ def determine_backend
       value = raw_hash[lookup_function]
       backends = BACKENDS
       custom_mappings = Rails.configuration.hdm[:custom_lookup_function_mapping]
-      backends = backends.deep_merge({ "lookup_key" => custom_mappings }) if custom_mappings.present?
+      backends = backends.deep_merge({ "lookup_key" => custom_mappings.stringify_keys }) if custom_mappings.present?
       backends.fetch(key).fetch(value).to_sym
     rescue KeyError
       raise Hdm::Error, "unknown backend #{value}"

test/models/hiera_data/hierarchy_test.rb

@@ -234,7 +234,7 @@ class HierarchyForCustomBackend < ActiveSupport::TestCase
 
       test "custom lookup function mapped to eyaml" do
         Rails.configuration.hdm[:custom_lookup_function_mapping] = {
-          "custom_eyaml_function" => "eyaml"
+          custom_eyaml_function: "eyaml"
         }
         hierarchy = HieraData::Hierarchy.new(raw_hash:, base_path: ".")
         assert_equal :eyaml, hierarchy.backend