PropCheck.measure

You're seeing just the function measure, go back to PropCheck module for more information.
Link to this function

measure(test, title, num)

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Specs

measure(test(), title(), number() | [number()]) :: test()

A function that collects numeric statistics on the produced instances.

The number (or numbers) provided are collected and some statistics over the collected sample are printed at the end of testing (in case no test fails), prepended with title, which should be an atom or string.