1. A system for generating an early indication of a fault in the operation of a computer program due, for example, to a coding error, or a fault in the operation of a computer based dedicated controller due to an error in its construction, design, programming, or due, for example, to a failed component, before the fault results in the generation of an incorrect output, said system comprising: means for monitoring output signals of a CPU of a data processing system under test; means for independently assigning to each and every location in a computer's memory space one code selected from a set of three or more codes, the code defining at least one condition which, if true when the memory location is accessed during the program's execution, is an indication of a fault in the operation of the program or controller; means for determining, on every access to a memory location during the program's execution, if the condition, defined by the code assigned to the memory location, is true when the memory location is being accessed; and means for generating an output indicating whether the condition is true.