1. A method, comprising: intercepting a first occurrence of an external function call made by a computer application program, the functional call intended for a shared library; identifying a test scenario corresponding to the function call, the test scenario comprising a plurality of simulated output parameters; providing, by a processing device, a first simulated output parameter of the plurality of simulated output parameters to the computer application program in response to the first occurrence of the function call for the computer application program to enter an error execution path, wherein the shared library does not provide an output parameter to the computer application program; receiving an indication of a behavior of the computer application program in response to the first simulated output parameter; intercepting a second occurrence of the external function call made by the computer application program; and providing a second simulated output parameter of the plurality of simulated output parameters to the computer application program in response to the second occurrence of the function call.