[net.lfn3/undertaker "0.1.5"]
A property testing library for Clojure and Java. If you've used test.check before you might want to start by reading Coming from test.check instead of this. Otherwise, if you're new to property based testing in general, or property testing in Clojure, read on.
Property based testing is based around invariants: things that will always be true about the results of running your code, regardless of the inputs to that code. That's fairly abstract, so lets look at an example:
(undertaker/defprop sum-should-be-greater-than-inputs {}
(let [a (undertaker/int)
b (undertaker/int)])
(is (< a (+ a b)))
(is (< b (+ a b))))So this is a very simple property based test that checks when we add two numbers that the result is greater each of
those numbers. This is a perfect example of the value of property testing, since at first glance it seems like this
test should pass, however it will fail if for instance a = 0 and b = -1. Typically Undertaker will not generate
this particular test case, but rather one with much more complicated test inputs such as a = -245645 and b = -12313.
Once a failing test case is located, Undertaker will attempt to shrink, or reduce the complexity of the inputs to be
as near to zero as possible.
Unlike other property testing libraries such as test.check, Undertaker allows to generate input for the test at any point during the test, rather than having to specify all the input up front. I think this makes it much easier to write tests, especially since it makes the generation process more like regular Clojure code.
It's been used at LMAX via undertaker-junit for several months. It's still under heavy and active development, and will continue to be so for the foreseeable future. API changes should be minimal and non-breaking, but of course, I don't want to make any guarantees about that until v1.0, and it's seen some use outside of LMAX.
At the moment the documentation is still fairly slim. Improving the documentation and the performance are my main focus at present. In the interim, the best guide for how to use the API is probably the usage tests here
David R. MacIver for writing Hypothesis and Hypothesis-Java without which there is approximately zero chance I would have realized there was a better way of doing property testing.
Reid Draper, Gary Fredericks and all of the contributors to test.check. test.check was where I started with property testing, and the place I "borrowed" big chunks of Undertaker's api from.
My employer, LMAX for paying for the significant amount time I've spent working on this thing. In particular Mike Barker for doing significant rubber duck duty.
Copyright © 2017 Liam Falconer
Distributed under the Apache License, Version 2.0