Stress testing stresses the system that demands resources in abnormal quantity, frequency, or volume. For instance, the test script may increased the frequency of input data to see how the modules perform or respond to the load. Another test case would be to maximum memory usage for a process. For instance, one thousand processes are acceptable for a particular operation system but one more process will pull the operating system performance down then it has exceeded the boundary that processes can run efficiency. Capacity planners will use stress tests to stress the system out so that it can determine if more disk is needed, more memory is needed, more processes are need, or system needs to be re-architect to handle the new load.
Stress testing works great with testing maximum workloads.
Back testing compares different versions of modules. The original version of a process is compared to the new version of a process to check for results. The results should only be the changed that would affect new process. If differences that are not to be changed need to be investigated further. Version 0 is compared to Version 1 and only changes desired should be the only differences.