Property Based Developer Testing

Session at CITCONNA2013Sessions

Proposed by Paul Holser

• Amounts to adding "for-all" style assertions about a function to some "there-exists" style tests.
• Works best on already-TDD'ed code. TDD builds up designs example by example. Hard to see the "for-all" statements without data point to triangulate from.
• Agitar does something similar -- execute code using lots of different kinds of inputs, possibly deriving interesting data points by inspecting the test subject itself...
• Works well on already "math-y" domains
• Drives you, if you're paying attention, away from Primitive Obsession and modeling things like SKUs, Prices, SSNs, etc. as first-class concepts. Otherwise generators miss too much, or try to create invalid things.

Literature

• Property Based TDD at SPA 2013
• The Practice of Theories: Adding "For-all" Statements to "There-exists" tests
• Property based testing for domain models
• Property-based testing: What is it?
• Real World Haskell: testing and quality assurance
• Beyond xUnit exampled-based testing: property-based testing with ScalaCheck
• Property-Based Testing Tools
• Theory-infected: Or How I Learned to Stop Worrying and Love Universal Quantification

Tooling:

Java

• junit-quickcheck
• QuickCheck
• JCheck

Scala

• ScalaCheck

Python

• Hypothesis
• qc

Ruby

• rushcheck
• rantly

Haskell

• QuickCheck

Erlang

• ProTest