Test for issue #129 are not working as required

[silkentrance]

We need to either

• export the method that safely installs the exit listener, e.g. via tmp.__internal.safely_install_listener
• or reimplement part of what jest does to sandbox packages during test runs

The latter is not an option as it requires us to reimplement a lot of code for sandboxing the imports.

The first option seems to be good as we can then call the method multiple times during our tests.

And even if one calls upon the internal, then we are still good as it will cause no harm.

[silkentrance]

Sigh, the tests are working as expected. Needed to get my head around them.