Fix text for the merge request lock system note

app/services/system_note_service.rb

@@ -593,7 +593,7 @@ module SystemNoteService
 
   def discussion_lock(issuable, author)
     action = issuable.discussion_locked? ? 'locked' : 'unlocked'
-    body = "#{action} this issue"
+    body = "#{action} this #{issuable.class.to_s.titleize.downcase}"
 
     create_note(NoteSummary.new(issuable, issuable.project, author, body, action: action))
   end

spec/services/merge_requests/update_service_spec.rb

@@ -127,10 +127,10 @@ describe MergeRequests::UpdateService, :mailer do
       end
 
       it 'creates system note about discussion lock' do
-        note = find_note('locked this issue')
+        note = find_note('locked this merge request')
 
         expect(note).not_to be_nil
-        expect(note.note).to eq 'locked this issue'
+        expect(note.note).to eq 'locked this merge request'
       end
 
       context 'when not including source branch removal options' do

spec/services/system_note_service_spec.rb

@@ -1145,4 +1145,42 @@ describe SystemNoteService do
       it { expect(subject.note).to eq "marked #{duplicate_issue.to_reference(project)} as a duplicate of this issue" }
     end
   end
+
+  describe '.discussion_lock' do
+    subject { described_class.discussion_lock(noteable, author)  }
+
+    context 'discussion unlocked' do
+      it_behaves_like 'a system note' do
+        let(:action) { 'unlocked' }
+      end
+
+      it 'creates the note text correctly' do
+        [:issue, :merge_request].each do |type|
+          issuable = create(type)
+
+          expect(described_class.discussion_lock(issuable, author).note)
+            .to eq("unlocked this #{type.to_s.titleize.downcase}")
+        end
+      end
+    end
+
+    context 'discussion locked' do
+      before do
+        noteable.update_attribute(:discussion_locked, true)
+      end
+
+      it_behaves_like 'a system note' do
+        let(:action) { 'locked' }
+      end
+
+      it 'creates the note text correctly' do
+        [:issue, :merge_request].each do |type|
+          issuable = create(type, discussion_locked: true)
+
+          expect(described_class.discussion_lock(issuable, author).note)
+            .to eq("locked this #{type.to_s.titleize.downcase}")
+        end
+      end
+    end
+  end
 end