Merge branch 'dz-mr-version-compare' into 'master'

Allow compare merge request versions

## What does this MR do?

Add new functionality to the merge request page. It allows you easily compare merge request versions in one click.  

## Are there points in the code the reviewer needs to double check?

## Why was this MR needed?

To improve code review experience. 

## Screenshots (if relevant)

See discussion

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [x] ~~API support added~~
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/13570

See merge request !6127

1 files changed, 37 insertions, 6 deletions

diff --git a/spec/features/merge_requests/merge_request_versions_spec.rb b/spec/features/merge_requests/merge_request_versions_spec.rb
index 577c910f11b..9e759de3752 100644
--- a/spec/features/merge_requests/merge_request_versions_spec.rb
+++ b/spec/features/merge_requests/merge_request_versions_spec.rb
@@ -11,8 +11,8 @@ feature 'Merge Request versions', js: true, feature: true do
   end
 
   it 'show the latest version of the diff' do
-    page.within '.mr-version-switch' do
-      expect(page).to have_content 'Version: latest'
+    page.within '.mr-version-dropdown' do
+      expect(page).to have_content 'latest version'
     end
 
     expect(page).to have_content '8 changed files'
@@ -20,18 +20,49 @@ feature 'Merge Request versions', js: true, feature: true do
 
   describe 'switch between versions' do
     before do
-      page.within '.mr-version-switch' do
+      page.within '.mr-version-dropdown' do
         find('.btn-link').click
-        click_link '6f6d7e7e'
+        click_link 'version 1'
       end
     end
 
     it 'should show older version' do
-      page.within '.mr-version-switch' do
-        expect(page).to have_content 'Version: 6f6d7e7e'
+      page.within '.mr-version-dropdown' do
+        expect(page).to have_content 'version 1'
       end
 
       expect(page).to have_content '5 changed files'
     end
+
+    it 'show the message about disabled comments' do
+      expect(page).to have_content 'Comments are disabled'
+    end
+  end
+
+  describe 'compare with older version' do
+    before do
+      page.within '.mr-version-compare-dropdown' do
+        find('.btn-link').click
+        click_link 'version 1'
+      end
+    end
+
+    it 'should has correct value in the compare dropdown' do
+      page.within '.mr-version-compare-dropdown' do
+        expect(page).to have_content 'version 1'
+      end
+    end
+
+    it 'show the message about disabled comments' do
+      expect(page).to have_content 'Comments are disabled'
+    end
+
+    it 'show diff between new and old version' do
+      expect(page).to have_content '4 changed files with 15 additions and 6 deletions'
+    end
+
+    it 'show diff between new and old version' do
+      expect(page).to have_content '4 changed files with 15 additions and 6 deletions'
+    end
   end
 end