Proposes a test strategy for FPGAs to be applied within FPGA-based fault-tolerant systems. We propose to make some configurable logic blocks (CLBs) under test and to implement the rest of the CLBs with the normal user data. In the target fault-tolerant systems, there are two phases (the functional phase and the test phase). In the functional phase, the system achieves its normal functionality, while in the test phase, the FPGA is tested. In this phase, the configuration data of the CLBs under test are shifted on-chip in parallel to other CLBs for achieving the test in these CLBs. All the CLBs are tested in a single test phase. The shifting process control, test application and test observation are achieved by the logic managing the fault tolerance (from outside the chip). The system returns to its normal phase after all the CLBs have been scanned by the test. The application of this approach reduces the fault tolerance cost (hardware, software, time, etc). The user is then able to periodically test the chip using only the data inside the chip and without destroying the original configuration data. No particular hardware is required for saving the test data on-board. Additionally, no particular software treatment is required for the test. The testing time is reduced enormously. Unfortunately, as a consequence of implementing two types of data on-chip, a 15% decrease in the chip functionality and a 2.5% delay overhead are noticed in the case of structures similar to a 20/spl times/20 Xilinx FPGA.