I saw a case of non-deterministic failure in CI that's almost
certainly caused by multiple threads being present when the thread
printer runs. In particular, a thread with `puma` in the stack was
present.
Although the test suite is single-threaded, nothing synchronizes the
joining of all threads between tests. While perhaps chasing such
non-determinism could be fruitful, doing so via the ThreadPrinter test
doesn't make sense; it'd have to be in a before/after/around
arrangement, e.g. in dispatcher_spec.rb:
describe "#start_cohort" do
after do
Thread.list.each { _1.join if _1 != Thread.current }
end
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