When a switch component exhibits symptoms of possible hardware failure, additional diagnostics tests should be performed to confirm the issue is hardware related and rule out other causes of the symptoms.
Some tests disrupt network activity, so it is important to verify that the test you run does not affect your current network traffic.
Runtime diagnostic checks can be run on demand or scheduled to run at a specific time. They can run continually in the background. When a module or supervisor exhibits failure symptoms or an error message is received, the test can usually be performed on demand.
http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps708/prod_white_paper0900aecd801e659f.html