To see the problem, you should just need to do npm install and then npm run test. What will happen is that the tests will gradually slow to a crawl and then fail to complete. If you really want to make it happen fast, you can add --maxWorkers=1 to the command for running the tests in the scripts section of package.json.

Things I've learned:

• Honeybadger's singleton is getting initialized once per test file, setting up its instrumentation each time.
• Commenting out the contents of Honeybadger's instrument function does fix the problem.
• Putting console statements into the callbacks from instrument shows them being called many times per test execution
• In jest-environment-jsdom-fourteen, the environment is also initialized once per test file. The environment appears to be creating a new jsdom_1.JSDOM instance, so I'm not sure how the event handlers are remaining each time.