Test cases for Helper in ember-cli application

I have created helper file in ember for formatting date using moment.js library. Helper has some if else conditions. When I generated this helper using ember-cli command, a test file also created. But i couldnt write test case inside it. When i run the test, it shows error that wbFormatDate (my helper name) is not a function. Have anybody faced this issue before? Please let me know the best practive to create test cases for helper in ember-cli application