Tests aimed at showing that a component or system does not 
work.Negative testing is related to the tester's attitutde 
rather than a specific test approach or test design 
technique,
e.g.testing with invalid input values or expections.

Test cases are written purposely to show that the program 
does not work.

Negative Test will be effective if it sone by an Experienced
Test Engineer, because negative Test case is generating When
applying  Test cases by Expecting intended output error.To
Do  a negative Test a Tester Should Have Following
Prerequisites ....

1.Domain Knowledge

2.Thorough Knowledge about Input-Output relationship

3.Good Understanding about Requirements

     For Negative Test usually we will create some Invalid
Situation  by using INvalid Input. If Test Result is Showing
a "Pass" .Surely it will be a Good Test case.

Thank You,,