Delay testing is important for high speed ICs.The main difficulty for delay testing comes from the huge number of paths and the large percentage of delay untestable paths.This paper presents an approach to delay testing with duplicating variable observation points

which provides a high path delay fault coverage by testing a small number of paths.The penalty that we should pay is a variable double observation at the output to identify the output transition time.This approach simplifies delay testing greatly in that the number of sample paths is linear to the number of gates in the circuit under test

despite of exponential growth in the number of paths.