Hi,

Load Testing and Performance Testing are Positive testings where as Stress Testing is negitive.

Letus take for example there is application which can handle 25 simulatenous user logins at a time. In load testing we will test the application for 25 users and how application is working in this stage, in performance testing we will concentrate on time taken to perform the operation. Where as in stress testing we will test with more users than 25 and the test will continue to any  number and we will check where the application is craching.