property-testing-for-fun-and-profit.md

title	author	patat
Property testing	James Santucci	wrap margins true left right 40 40

Welcome

• Matt Bachmann on Hypothesis
• Old RF ADR on testing

This talk

• tests are programs that verify your expectations about other programs
• property testing can save you from having to state your expectations separately about a lot of similar cases
• you can property test anywhere

What's testing

• programs that verify some expected behavior occurs under known conditions

Programs that verify

• is this a test?

from .lib import foo

def test_foo():
    result = foo(3, 4)
    assert result == 7

Programs that verify

• is this a test?

from .lib import foo

def test_foo():
    result = foo(3, 4)
    assert result == 7, "oh no"

$ python -m pytest

Programs that verify

• is this a test?

from .lib import foo

def should_work():
    result = foo(3, 4)
    assert result == 7, "oh no"

if __name__ == '__main__':
    should_work()

$ python thing_that_should_work.py

Programs that verify

• is this a test?

$ sbt compile

A library

• tiny-test

When should you property test?

• when there are laws
• when you have an oracle
• when you have a black box
• when you have an expected round trip

Property testing everywhere

• haskell
• purescript
• scala
• elm
• rust
• C
• python
• old javascript
• new javascript
• R
• julia
• Java

This talk

• tests are programs that verify your expectations about other programs
• property testing can save you from having to state your expectations separately about a lot of similar cases
• you can property test anywhere

✅