Add feature test for merge request version

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

spec/features/merge_requests/merge_request_versions_spec.rb

+require 'spec_helper'
+
+feature 'Merge Request versions', js: true, feature: true do
+  before do
+    login_as :admin
+    merge_request = create(:merge_request, importing: true)
+    merge_request.merge_request_diffs.create(head_commit_sha: '6f6d7e7ed97bb5f0054f2b1df789b39ca89b6ff9')
+    merge_request.merge_request_diffs.create(head_commit_sha: '5937ac0a7beb003549fc5fd26fc247adbce4a52e')
+    project = merge_request.source_project
+    visit diffs_namespace_project_merge_request_path(project.namespace, project, merge_request)
+  end
+
+  it 'show the latest version of the diff' do
+    page.within '.mr-version-switch' do
+      expect(page).to have_content 'Version: latest'
+    end
+
+    expect(page).to have_content '8 changed files'
+  end
+
+  describe 'switch between versions' do
+    before do
+      page.within '.mr-version-switch' do
+        find('.btn-link').click
+        #find('a', text: '6f6d7e7e').click
+        click_link '6f6d7e7e'
+      end
+    end
+
+    it 'should show older version' do
+      page.within '.mr-version-switch' do
+        expect(page).to have_content 'Version: 6f6d7e7e'
+      end
+
+      expect(page).to have_content '5 changed files'
+    end
+  end
+end