Abstract: A decoder/analyzer test unit capable of rapidly identifying and isolating a failure or fault detected during a sequence of numerous discrete tests of a digital computer in an aircraft flight guidance system is disclosed. The test unit broadly comprises a means for comparing for coincidence of a signal representing a satisfactory result of a discrete test of a computer during a test sequence and another signal that initiated the particular discrete test, means for stopping the computer test sequencing when there is a lack of coincidence of the compared signals for any particular discrete test, and step counter means for counting and indicating the particular test that the computer is undergoing. Test points connecting with identified connections in the computer under test are provided on the test unit for troubleshooting purposes. The test unit can be operated in automatic, continuous and manual modes of operation.