process.exit() from user code breaks test run

If the user code called in a test runs process.exit(<code>), Jest's behaviour depends on:

• whether one or multiple test files are run
• the order(?) in which the tests are executed

Demos

Just the exiting test

Just the passing test:

Both, where the exiting test simply exits

Both, where the exiting test causes the run to hang (having changed only the name of the passing test file)

With the diff from #6714 applied:

Notes

• Running Jest with --runInBand makes the runner always exit immediately after process.exit(1) is called.