PropCheck.trap_exit

You're seeing just the macro trap_exit, go back to PropCheck module for more information.
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trap_exit(prop)

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If the code inside prop spawns and links to a process that dies abnormally, PropEr will catch the exit signal and treat it as a test failure, instead of crashing.

trap_exit cannot contain any more wrappers.

iex> use PropCheck
iex> quickcheck(
...>   trap_exit(forall n <- nat() do
...>     # this must fail
...>     _pid = spawn_link(fn() -> n / 0 end)
...>     # wait for arrivial of the dieing linked process signal
...>     :timer.sleep(50)
...>     true #
...>   end)
...> )
false