Figure out how to run inline tests

I *think* that Jest is breaking my changes to global between test runs, not a problem in vm2 (I think it uses eval) but when creating a new module and compiling it `global` is reset.

This is less of an issue in danger, but much more of an issue in Peril.

Perhaps in tests we could not edit globals and use `jest.mock` on a "danger" import?

Start by reproducing the inline-test behavior described with Jest, a newly compiled vm2 module, and changes to global, comparing Danger and Peril contexts. Trace how the test setup creates modules and isolates globals; done means the behavior is understood and the issue has a concrete, reproducible resolution for test isolation.

Written by the indexing model from the issue text.