issue with gem 'minitest-hyper'

Am using minitest-hyper gem to produce result of testcases in html. but when i run my test cases am getting below issue

1)When i run TEST_OPTS="--html" rake test:units

2)am getting invalid option: --html Test::Unit automatic runner.

3) am using gem 'gem "minitest-hyper", :require => false' gem 'rails', git: 'http://ift.tt/209EpDf', branch: '3-2-stable' ruby 2.1.2

4)how to solve this question , i tried for sample its working but in project its not working.