We propose an unambiguous instruction cache software-based self-testing methodology that can generate a reliable result to precisely determine the test passed or not. We present testing cases that cause ambiguous cache testing results and propose five principles of test pattern selection to prevent these situations from occurring. To preserve the order of March sequence in testing an I-cache, we leverage cache bank and cache disable operations. In this way, we are able to implement any March algorithm without violating the sequence order. Finally, we present a case study for ARM v5 ISA processor that has an 8KB instruction cache. We use the March C- algorithm and achieve 100% of inter-word coverage and more than 97% of intra-word coverage evaluated by the RAMSES simulator.