Added ref switcher enter key tests

spec/features/projects/ref_switcher_spec.rb

+require 'rails_helper'
+
+feature 'Ref switcher', feature: true, js: true do
+  include WaitForAjax
+  let(:user)      { create(:user) }
+  let(:project)   { create(:project, :public) }
+
+  before do
+    project.team << [user, :master]
+    login_as(user)
+    visit namespace_project_tree_path(project.namespace, project, 'master')
+  end
+
+  it 'allow user to change ref by enter key' do
+    click_button 'master'
+    wait_for_ajax
+
+    page.within '.project-refs-form' do
+      input = find('input[type="search"]')
+      input.set 'expand'
+
+      input.native.send_keys :down
+      input.native.send_keys :down
+      input.native.send_keys :enter
+
+      expect(page).to have_content 'expand-collapse-files'
+    end
+  end
+end