Defect injection -- Deliberately inserted defects, inserted at any phase, and intended to determine the effectiveness of quality assurance, testing, or defect containment discipline. Also known as "defect seeding".
An injected defect is adding defects to a system on purpose during testing, to test and verify that the system behaves as expected in those situations.
This is good testing practice, and nothing that should be reduced or avoided.
Examples of such defects can be:
1. Introducing unreliable network traffic.
2. Testing with a full hard drive.
3. Testing with some hardware component malfunction.