When you are writing test cases , whether they are unit
tests, tests for test-driven development, regression tests,
or any other kind, there are some functions you will find
yourself doing each time.  These include the basics of an
application, a mechanism for launching tests, and a way to
report results.  You could write these functions each time
you start testing a new feature or you could write them once
and utilize them every time.  A test harness, at its most
simple, is just that—a system to handle the elements you’ll
repeat each time you write a test. 

The typical objectives of a test harness are to:

    

The test harness should incluse the following capabilities:-
    * A standard way to specify setup (i.e., creating an
artificial runtime environment) and cleanupAutomate the
testing process.
    * A method for selecting individual tests to run, or all
tests.
    * A means of analyzing output for expected (or
unexpected) results.
    * A standardized form of failure reporting.

A Test harness  is collection of software and testdata 
which is used to test the application with different test 
data with pass and fail as results.