Allow applications to overide filter name via env

** Why are these changes being introduced:

* The nice_labels method in the filter helper defines static names for
  each possible filter category, but the GDT project makes it likely
  that these names may need to vary by application due to the nature of
  the records available (i.e. "content type" versus "data type").

** Relevant ticket(s):

* https://mitlibraries.atlassian.net/browse/gdt-128

** How does this address that need:

* This adds support for loading the filter name from ENV, using a set of
  variables listed in the README.

** Document any side effects to this change:

This is not a side effect, but a point of hesitation. I'm unsure if we
need tests for _each_ ENV override in nice_labels. Right now I've
written one to confirm that "Content type" is the default, and one to
confirm that it can be overriden - for that category only. It feels
like a bit of overkill to test each of the seven categories (and then
need to write more tests as new categories are added to the API) - but
this leaves open the possibility that the overrides - which are not
likely to be heavily used - might break in a way that we do not realize
initially.

I take some solace in the fact that the defaults we provide are "okay",
and that there will be stakeholders watching for the overridden values -
so any future problem should be caught relatively quickly - but I'm open
to contrasting perspectives here.

Author: matt-bernhardt

README.md

@@ -52,6 +52,13 @@ change as part of the work.
 - `ABOUT_APP`: If populated, an 'about' partial containing the contents of this variable will render on 
 `basic_search#index`.
 - `ACTIVE_FILTERS`: If populated, this list of strings defines which filters are shown to the user, and the order in which they appear. Values are case sensitive, and must match those used in the TIMDEX GraphQL query. Extraneous values will be ignored. If not populated, all filters will be shown.
+- `FILTER_CONTENT_TYPE`: The name to use instead of "Content type" for that filter / aggregation.
+- `FILTER_CONTRIBUTOR`: The name to use instead of "Contributor" for that filter / aggregation.
+- `FILTER_FORMAT`: The name to use instead of "Format" for that filter / aggregation.
+- `FILTER_LANGUAGE`: The name to use instead of "Language" for that filter / aggregation.
+- `FILTER_LITERARY_FORM`: The name to use instead of "Literary form" for that filter / aggregation.
+- `FILTER_SOURCE`: The name to use instead of "Source" for that filter / aggregation.
+- `FILTER_SUBJECT`: The name to use instead of "Subject" for that filter / aggregation.
 - `GDT`: Enables features related to geospatial data discovery. Setting this variable with any value will trigger GDT
 mode (e.g., `GDT=false` will still enable GDT features). Note that this is currently intended _only_ for the GDT app and
 may have unexpected consequences if applied to other TIMDEX UI apps.

app/helpers/filter_helper.rb

@@ -21,13 +21,13 @@ def add_filter(query, filter, term)
 
   def nice_labels
     {
-      contentTypeFilter: 'Content type',
-      contributorsFilter: 'Contributor',
-      formatFilter: 'Format',
-      languagesFilter: 'Language',
-      literaryFormFilter: 'Literary form',
-      sourceFilter: 'Source',
-      subjectsFilter: 'Subject'
+      contentTypeFilter: ENV.fetch('FILTER_CONTENT_TYPE', 'Content type'),
+      contributorsFilter: ENV.fetch('FILTER_CONTRIBUTOR', 'Contributor'),
+      formatFilter: ENV.fetch('FILTER_FORMAT', 'Format'),
+      languagesFilter: ENV.fetch('FILTER_LANGUAGE', 'Language'),
+      literaryFormFilter: ENV.fetch('FILTER_LITERARY_FORM', 'Literary form'),
+      sourceFilter: ENV.fetch('FILTER_SOURCE', 'Source'),
+      subjectsFilter: ENV.fetch('FILTER_SUBJECT', 'Subject')
     }
   end
 

test/helpers/filter_helper_test.rb

@@ -67,6 +67,19 @@ class FilterHelperTest < ActionView::TestCase
     assert_nil nice_labels[needle]
   end
 
+  test 'nice_labels will use a value from ENV instead of the default if provided' do
+    label = 'Content type'
+    ClimateControl.modify FILTER_CONTENT_TYPE: nil do
+      needle = :contentTypeFilter
+      assert_equal label, nice_labels[needle]
+    end
+    label = 'Custom label'
+    ClimateControl.modify FILTER_CONTENT_TYPE: label do
+      needle = :contentTypeFilter
+      assert_equal label, nice_labels[needle]
+    end
+  end
+
   test 'remove_filter will remove a specific filter parameter from a search URL' do
     original_query = {
       page: 1,