How to print failed assertions to a file?

Hi All,

I've 10 testcase, each testcase have 2 or 3 assertions. What I need is if I run the entire 10 testcases at time and if any one assertion fails in any one of the testcases, I need to print the failed assertion to separate external file. So my external file should have only failed assertions.

Any help on this?

Regards,
Naveen