forcbly injecting bug and testing the functionaliy

That's right, Srikar!!
Adding to it..

With mutation testing, the system/program under test is 
changed to create a faulty version called a mutant. You 
then run the mutant program through a suite of test cases, 
which should produce new test case failures. If no new 
failures appear, the test suite most likely does not 
exercise the code path containing the mutated code, which 
means the program isn't fully tested. You can then create 
new test cases that do exercise the mutant code.

This is one of the White Box Testing Technique . Generaly 
programmer are following this tehnique to test the change 
in the programme t estimate the correctness & completeness 
of the programme.

  for example
  1. if all tests passed in the programme that is good 
programme.
 2. If all tests passed but in the programe some change is 
there .don't say passed. this is not a good teting
3. in alltests passed except change test failed. this is 
the complete testing.

Hi,
In mutation testing we create a duplicate copy of the code
that is called as mutant and do some changes in the codes in
the mutant copy and then we test and check weather the
changes are been detected or not and whether it is creating
any effect on the original copy of the code or not.If the
changes are being detected then it is called as killed mutant.

Plz correct me if i m wrong..
Nitin Verma
nitin9360@gmail.com

Mutation testing also called mutation analysis is a method 
of software testing, which involves modifying program's 
source code in small ways. These, so-called mutations, are 
based on well-defined mutation operators that either mimic 
typical user mistakes (such as using the wrong operator or 
variable name) or force the creation of valuable tests. The 
purpose is to help the tester develop effective tests or 
locate weaknesses in the test data used for the program or 
in sections of the code that are seldom or never accessed 
during execution.