when package:massiv-test

Conditional execution of Applicative expressions. For example,

when debug (putStrLn "Debugging")

will output the string Debugging if the Boolean value debug is True, and otherwise do nothing.

Performs an IO action after the last failure of a property.

Performs an IO action every time a property fails. Thus, if shrinking is done, this can be used to keep track of the failures along the way.