1. A computer-implemented method, comprising: storing a first input, a first function and a corresponding first output type, wherein the first output type is a result of a prior execution of the first function with the first input for a first test of operation of computer code; determining during execution of a second test of operation of computer code whether a second input type for the second test of operation of computer code matches the first output type; selectively executing again the first function with the first input in response to a determination that the second input type matches the first output type, to generate a first output; and performing the second test using the first output of the selectively executing again the first function as a second input.