Fault-based testing technique is

Explanation

Mutation testing is the standard fault-based technique: small faults (mutations) are deliberately seeded into the program to create mutants, and the test suite is judged by how many mutants it "kills" – that is, by the proportion of seeded faults it detects. The whole method is organised around hypothesised faults, which is what "fault-based" means. Unit testing is a level of testing, beta testing is a form of acceptance testing by end users, and stress testing is a performance test that pushes the system beyond its normal load; none of them is driven by seeded faults. Hence option 4.