Do you write unit tests for your code? What are the challenges you have in having unit tests? Please share your experiences

Automated unit testing is very useful as it will reduce unit testing time significantly. Identify test cases and prepare test data for automated testing is most challenging. We are using JUnit for automated unit testing.  

you must use unit test on your code because that best for programer to find error during occurrence

that give more efficient to your code, fastest to find error

You need to focus mainly in doing "Test-driven development".

Of course you have to use Unit Tests for your code, but not all your code!

if there is a certain business senario you put for a function you should use unit test and code coverage to make sure that all the senarios are covered.

it might consume some time, but you should plan them from the very begining of the project