Design for test sits between design and manufacturing. The DFT engineer adds the structures that let every manufactured chip be tested quickly and thoroughly, and generates the patterns used on the tester.
The work covers defining a DFT architecture, inserting scan chains and compression, generating ATPG patterns to meet coverage targets, adding memory built-in self-test and boundary scan, and validating it all in simulation. DFT engineers work with RTL, physical design and product test teams, and often support silicon debug and pattern bring-up on the tester.
DFT choices made at design stage directly shape test cost and yield on the factory floor, which is why engineers who understand both design and test are especially valuable.