Update merge request page object and selectors

These are changes from EE that are also relevant to CE from:
https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/8372

app/views/projects/merge_requests/_mr_title.html.haml

@@ -37,6 +37,6 @@
               = link_to 'Reopen', merge_request_path(@merge_request, merge_request: { state_event: :reopen }), method: :put, class: 'reopen-mr-link', title: 'Reopen merge request'
 
       - if can_update_merge_request
-        = link_to 'Edit', edit_project_merge_request_path(@project, @merge_request), class: "d-none d-sm-none d-md-block btn btn-grouped js-issuable-edit"
+        = link_to 'Edit', edit_project_merge_request_path(@project, @merge_request), class: "d-none d-sm-none d-md-block btn btn-grouped js-issuable-edit qa-edit-button"
 
       = render 'shared/issuable/close_reopen_button', issuable: @merge_request, can_update: can_update_merge_request, can_reopen: can_update_merge_request

qa/qa/page/merge_request/show.rb

@@ -55,6 +55,10 @@ module QA
           element :labels_block
         end
 
+        view 'app/views/projects/merge_requests/_mr_title.html.haml' do
+          element :edit_button
+        end
+
         def fast_forward_possible?
           !has_text?('Fast-forward merge is not possible')
         end
@@ -163,6 +167,10 @@ module QA
           all_elements(:discussion_reply).last.click
           fill_element :reply_input, reply_text
         end
+
+        def edit!
+          click_element :edit_button
+        end
       end
     end
   end

qa/qa/resource/merge_request.rb

@@ -11,7 +11,9 @@ module QA
                     :target_branch,
                     :assignee,
                     :milestone,
-                    :labels
+                    :labels,
+                    :file_name,
+                    :file_content
 
       attribute :project do
         Project.fabricate! do |resource|
@@ -35,8 +37,8 @@ module QA
           resource.branch_name = target_branch
           resource.remote_branch = source_branch
           resource.new_branch = false
-          resource.file_name = "added_file.txt"
+          resource.file_name = file_name
-          resource.file_content = "File Added"
+          resource.file_content = file_content
         end
       end
 
@@ -48,6 +50,8 @@ module QA
         @assignee = nil
         @milestone = nil
         @labels = []
+        @file_name = "added_file.txt"
+        @file_content = "File Added"
       end
 
       def fabricate!