[Tests] groups

[michellexliu]

spec/controllers/groups_controller_spec.rb

• [Render test] index
• [Render test] show
• [Render test] new
• [Functionality test] create
• [Functionality test] update
• [Functionality test] destroy
• [Functionality test] import
• [Functionality test] add
• [Functionality test] join
• [Functionality test] leave