A processor-implemented method for diagnostic testing using an expected result parameter is provided. The processor-implemented method may include establishing a known system environment associated with a function under test and setting the expected result parameter corresponding to the function under test and the known system environment. A call is issued by the processor to execute the function under test. Before returning to the caller, the function under test compares an expected result value to an actual result value. The function under test determines an error based on the actual result value being different from the expected result value and performs a low-level diagnostic based on the determined error. Then the processor receives a return value from the function under test based on the issued call.