Rename test file
Add test => X_X .shouldThrowError is a function
Add test => X_X .shouldNotThrowError when function() is undefined
Implement X_X .shouldThrowError is a function

- Bug =>
  - testHelper should log `X_X .shouldThrowError is a function: true`
  - testHelper logs `is a function: true`
Fix bug in previous commit

- need to add test coverage for this commit!