1. An isolation system comprising: logic configured to: receive original product code, the original product code containing a plurality of original methods, at least one original method being dependent on external functionality that is not under control of a test being performed; receive selection information which defines a subset of selected original methods of the plurality of original methods to be processed; at a first time, convert each of the selected original methods in the subset of selected original methods of the plurality of original methods into corresponding modified parts declaring type-safe property properties having delegate types; at a second time, determine that an individual selected original method in the subset of selected original methods of the plurality of original methods has a corresponding individual modified part that has already been converted and stored; and use the individual modified part that has already been converted and stored to invoke associated detour code instead of the individual selected original method; and one or more processing devices configured to execute the logic.