Complete unit tests

[afshinm]

We should write unit tests for project, as far as you know there's only one unit test in the project that really do nothing: https://github.com/sallar/jDateTime/blob/master/Tests/JDateTimeTest.php#L19

[sallar]

Yes indeed. Unit tests are too important for this project because every merge or change can possibly break the whole script. But I'm so dumb when it comes to unit testing.

[afshinm]

Keep it simple, I think we could declare a local variable with a sample Gregorian datetime in setUp function and do all tests (e.g. Convert to Jalali date) in the JDateTimeTest.php file.