Add a test for issue sentence generation

app/helpers/merge_requests_helper.rb

@@ -42,4 +42,8 @@ module MergeRequestsHelper
       "Branches: #{@merge_request.source_branch} #{separator} #{@merge_request.target_branch}"
     end
   end
+
+  def issues_sentence(issues)
+    issues.map { |i| "##{i.iid}" }.to_sentence
+  end
 end

app/views/projects/merge_requests/show/_state_widget.html.haml

@@ -37,5 +37,5 @@
         %i.icon-ok
         Accepting this merge request will close #{@closes_issues.size == 1 ? 'issue' : 'issues'}
         = succeed '.' do
-          != gfm(@closes_issues.map { |i| "##{i.iid}" }.to_sentence)
+          != gfm(issues_sentence(@closes_issues))
 

spec/helpers/merge_requests_helper.rb

+require 'spec_helper'
+
+describe MergeRequestsHelper do
+  describe :issues_sentence do
+    subject { issues_sentence(issues) }
+    let(:issues) do
+      [build(:issue, iid: 1), build(:issue, iid: 2), build(:issue, iid: 3)]
+    end
+
+    it { should eq('#1, #2, and #3') }
+  end
+end