The document discusses property-based testing for services in Scala. It introduces property-based testing as an alternative to example tests that can generate random inputs to test definitions of how a program should behave. The document provides an example of generating test data using Scalacheck, writing properties to define expected outputs, and using for-comprehensions to combine generated values into more complex types for testing.

1. Property-Based Testing
for Services
in Scala
StrangeLoop, 24 September 2015
@jessitron

2. Property-Based Testing
for Services
in Scala
vs example tests

3. Property-Based Testing
for Services
in Scala
vs example tests
not only mathy things
& Scalacheck

4. why are we here?
Testing

5. why are we here?
Go faster! Don't break things!

6. why do we test?

7. why do we test?
confidence that it works
define "it works"
drive good design

8. confidence that it works
define "it works"
drive good design

9. How do we know it?
What do we know?

10. what will we do today?

11. what will we do today?
Learn prerequisites
See the application under test
Write a test together

12. input
output
output
example tests
side effects

13. example tests
input
outputoutput

14. example tests
input
outputoutput
input
outputoutput
input
outputoutput

15. input
output

16. output

17. generate input
runrepeatedly
track failures
narrow down cause
group properties together

18. generate input
runrepeatedly
track failures
narrow down cause
group properties together
Scalacheck (or Scalatest)
scalacheck.Gen
Prop
Shrink

19. val house = Item("house")
case class Item(name : String)
listOfItems.map {
item =>
item.name
}
item.name

20. listOfItems.map {
item =>
item.name
}
listOfItems.map {
item =>
item.name
}

21. listOfItems.map {
item =>
item.name
}
listOfItems.map(item => item.name)listOfItems.map(item => item.name)

22. listOfItems.map( _.name )
listOfItems.map {
item =>
item.name
}
listOfItems.map(item => item.name)

23. listOfItems.map {
item =>
item.name
}
listOfItems.map {
item =>
item.name
}

24. for {
item <- listOfItems
} yield item.name
listOfItems.map {
item =>
item.name
}

25. for {
item <- listOfItems
} yield item.name
for-comprehension

26. for {
item <- listOfItems
} yield item.name
List[Item]
List[String]

27. for {
item <-
} yield item.name
itemGenerator

28. Gen[Item]
Gen[String]
for {
item <-
} yield item.name
itemGenerator

29. Gen[Item]
Gen[LineItem]
for {
item <- itemGenerator
price <- priceGenerator
} yield LineItem(item, price)
Gen[Price]