Common factors in deciding when to stop are:
Deadlines (release deadlines, testing deadlines, etc.)
Test cases completed with certain percentage passed
Test budget depleted
Coverage of code/functionality/requirements reaches a specified point
Bug rate falls below a certain level
Beta or alpha testing period ends
Deadlines (release deadlines, testing deadlines, etc.)
Test cases completed with certain percentage passed
Test budget depleted
Coverage of code/functionality/requirements reaches a specified point
Bug rate falls below a certain level
Beta or alpha testing period ends
Comments