We present a tight integration of the language of types and function
specifications of Erlang with property-based testing. To achieve this
integration we have developed from scratch PropEr, an open-source
QuickCheck-inspired property-based testing tool. We present technical
details of this integration, most notably how the conversion of
recursive types into appropriate generators takes place and how
function specifications can be turned automatically into simple
properties in order to exercise the code of these functions. Finally,
we present experiences and advice for the proper use of PropEr.