HI all, 
Request you to give a detaild explanation... if possible provide any snippet code. thanks 

i am keep on hitting while deploying classes into production  Organigaion code coverage is 45%. 
I noticed that some classes and triggers have 0% code coverage. 

1.How it could be possible to deploy a calss having 0% code coverage??. 
2. there is no test classes for few classes.. How it could be possible? 
3. for few classes have hidden code... how to sort out managed packes code coverage problem??
4. unmanaged packages have test classes and methods  in the apex class?? ... does it creating 0% code coverage issue to the classes??