Don't display Document Collection withdrawn documents

This brings government-frontend in line with Whitehall.

Trello:
https://trello.com/c/IFfWVlb6/533-filter-out-withdrawn-documents-in-document-collections-medium

Follow-up to:

- alphagov/govuk-content-schemas#454
- alphagov/publishing-api#627

Depends on:

- alphagov/govuk-content-schemas#459

app/presenters/document_collection_presenter.rb

@@ -16,9 +16,14 @@ def contents
   end
 
   def groups
-    content_item["details"]["collection_groups"].reject do |group|
-      group_document_links(group).empty?
-    end
+    content_item["details"]["collection_groups"]
+      .reject { |group|
+        group_document_links(group).empty?
+      }
+      .map { |group|
+        group["documents"] = reject_withdrawn_documents(group)
+        group
+      }
   end
 
   def group_document_links(group)
@@ -50,4 +55,10 @@ def group_title_id(title)
   def documents_hash
     @documents_hash ||= Array(content_item["links"]["documents"]).map { |d| [d["content_id"], d] }.to_h
   end
+
+  def reject_withdrawn_documents(group)
+    group_documents(group)
+      .reject { |document| document["withdrawn"] }
+      .map { |document| document["content_id"] }
+  end
 end

test/presenters/document_collection_presenter_test.rb

@@ -124,4 +124,21 @@ class GroupWithDocumentsWhenThereIsNoLinksDocuments < TestCase
       assert_empty group_with_missing_documents
     end
   end
+
+  class GroupWithDocumentsWhenThereAreWithdrawnDocuments < TestCase
+    test "does not present withdrawn documents" do
+      presenter = presented_item(
+        "document_collection_with_withdrawn_links_documents"
+      )
+
+      groups_without_withdrawn_documents = presenter.groups.first["documents"]
+
+      number_of_documents_that_have_withdrawn_false = 2
+
+      assert_equal(
+        groups_without_withdrawn_documents.size,
+        number_of_documents_that_have_withdrawn_false
+      )
+    end
+  end
 end