Avoid multiple module instances

[tslocke]

I get intermittent test failures in a project that uses ProseMirror. This is a known issue with ProseMirror if more than once instance of the module prosemirror-state is loaded.

From the command line, this seems to only happen on the first run. But using Wallaby, it happens all the time.

Is there a way to ensure a given module is only loaded once?

[tslocke]

Quick follow-up question - isn't having multiple instances of a module loaded going to be a bigger problem?

e.g. I think instanceof tests can potentially return false in the test environment, when they would be true in prod/dev.