Please let us know what the update is. If it's from Windows Update, you can right click on the update in order to get it's details.

Stress tests are normally OK to run on a well-behaved system.
If you're concerned about them, then watch the PC closely.
If it starts doing something wrong, then exit the tests.
If you can't exit the test, turn the computer off.
If you can't turn the computer off, remove the plug from the wall in order to shut the system down.