You seem to misunderstand the original intent of chysn's question. To be sure, even I explicity checked for the reasons in my first answer, but regardless:D-Type wrote:... Forth ...
The matter at hand does not involve executing script-like actions for tests, mostly from an empty start-up environment - something, which could be done on the VIC-20 with BASIC, machine language, any mixture of the latter two, (cross-)compiled C, any of the available Forths, or any other language implementation one could think of.
Rather, chysn wants to test already built code with pre-crafted input (which normally would come from keyboard, but now is delivered from a file) and wants to check the program's output (which normally goes to screen, but is stored in another file instead) against a 'known-good' instance of that output. In my answer, I pointed chysn to the relevant OS calls, which duly solved the question in the way he asked for.
In short, it's not about running code as such (in any language of choice), but rather providing an environment where I/O of a client program is redirected. On the CBM, this is functionality already provided by the KERNAL and has no specific binding to any language.