In this paper, C-testability conditions based on Realistic Sequential Cell Fault Model (RS-CFM) [3] are proposed and applied to the block FIR filters. Based on RS-CFM, an ILA is said to be C-testable for cell delay faults if it is possible to apply all SIC (single input change) pairs [2] of a cell to each cell of the array in such a way that the number of test pairs for the array is a constant. A novel design-for-testability technique based on the functional bijectivity property [1] is used to make the FIR array C-testable for delay faults. C-testability conditions guarantee 100% single-cell-fault and cell-delay-fault testability with a constant number of test patterns. The hardware overhead is about 5.66% to make it C-testable for cell delay faults. The number of test patterns is 80 regardless of the word length, filter order, and the block size. It is only 31% of that for pseudoexhaustive testing of the FIR filters. The reduction of test generation complexity is significant. Since the derived 80 two-pattern tests include the exhaustive test patterns for functional testing of the ILA, combinational faults can also be detected.