Best way to create a "fresh and empty" Node.js JavaScript context within the same process?

Question for Node.js and v8 experts.

I'm developing a new version of the Siesta testing tool.

By default, Siesta runs every test in the newly created Node.js process. However, I'd like to avoid the overhead of spawning a new process and instead provide the ability to run the test in the empty JavaScript context.

Such context can be created with the built-in vm module. However, the context created in this way is an empty JavaScript context, not an empty Node.js context. For example, it does not have global variable process:

> require('vm').runInNewContext('process')
evalmachine.<anonymous>:1
process
^

Uncaught ReferenceError: process is not defined
    at evalmachine.<anonymous>:1:1
    at Script.runInContext (vm.js:143:18)
    at Script.runInNewContext (vm.js:148:17)
    at Object.runInNewContext (vm.js:303:38)
    at REPL30:1:15
    at Script.runInThisContext (vm.js:133:18)
    at REPLServer.defaultEval (repl.js:484:29)
    at bound (domain.js:413:15)
    at REPLServer.runBound [as eval] (domain.js:424:12)
    at REPLServer.onLine (repl.js:817:10)
> 

So question is - what is the best way to create a fresh and empty Node.js context within the same process? I'd expect such context to have all regular globals, like process, require etc. Plus, I'd expect such context to have a separate and initially empty modules cache, so that even if some module is loaded in the main context, it will be loaded again in the new context.

Of course I could map the globals from the main context to the new context, but that would mean those globals are shared between contexts, and I'm aiming for context isolation. Plus the modules cache will be shared as well.

I believe the difference between JavaScript and Node.js context is that the latter is initialized with a certain script. Is it possible to obtain the sources of that script somehow and execute it in the new context?

Thank you!

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