How to write test cases for ensuing stream's/socket's closure either in catch block or finally block

[bhallamudi kamesh]

Hi All,
  How to write test cases for the scenarios such as throwing an IOException 
from the try block and ensuing that corresponding stream's/socket's closure 
either in catch block or in finally block.
  Do we need to write test cases for these scenarios in order to submit patches?

  Thanks in advance

With Regards,
Bh.V.S.Kamesh.