Property-Based Testing with PropEr, Erlang, and Elixir

Implementing Specials

So we have a more complex generator for specials, and a basic checkout implementation that doesn’t consider specials at all. We have everything we need to get started on implementing specials. Our first step should be making sure our test actually fails eventually, as a sanity check to know it’s good at detecting bad cases:

$ rebar3 proper
build information and other properties
===> Testing prop_checkout:prop_special()
......!
Failed: After 7 test(s).
{[[0],[6,1],[0],[0],[6,1],[6,1],[6,1],[0],[6,1],[6,1],[0],[6,1],[6,1],[6,1],
[6,1],[6,1],[6,1],[6,1],[6,1],[0],[6,1],[6,1],[6,1],[0],[6,1],[0],[0],[6,1],
[6,1],[6,1],[6,1],[0],[0],[0],[6,1],[6,1],[0]],20,[{[0],-2},{[6,1],1}],
[{[0],2,3},{[6,1],5,0}]}