Hspec is a framework for Behavior-Driven Development (BDD) in Haskell. BDD is an approach to software development that combines Test-Driven Development, Domain-Driven Design, and Acceptance Test-Driven Planning. Hspec helps you do the TDD part of that equation, focusing on the documentation and design aspects of TDD.
Hspec (and the preceding intro) are based on the Ruby library RSpec. Much of what applies to RSpec also applies to Hspec. Hspec ties together descriptions of behavior and examples of that behavior. The examples can also be run as tests and the output summarizes what needs to be implemented.
import Test.Hspec import Test.QuickCheck import Test.HUnit main :: IO () main = hspec spec
Since the specs are often used to tell you what to implement, it's best to start with undefined functions. Once we have some specs, then you can implement each behavior one at a time, ensuring that each behavior is met and there is no undocumented behavior.
unformatPhoneNumber :: String -> String unformatPhoneNumber = undefined formatPhoneNumber :: String -> String formatPhoneNumber = undefined
spec :: Spec spec = do describe "unformatPhoneNumber" $ do
Bool can be used as an example.
it "removes dashes, spaces, and parenthesies" $ unformatPhoneNumber "(555) 555-1234" == "5555551234"
pending function marks a behavior as pending an example. The example
doesn't count as failing.
it "handles non-US phone numbers" $ pending "need to look up how other cultures format phone numbers"
Assertion can be used as an example.
it "converts letters to numbers" $ do let expected = "6862377" actual = unformatPhoneNumber "NUMBERS" actual @?= expected
Property can be used as an example.
it "can add and remove formatting without changing the number" $ property $ forAll phoneNumber $ \n -> unformatPhoneNumber (formatPhoneNumber n) == n phoneNumber :: Gen String phoneNumber = do n <- elements [7,10,11,12,13,14,15] vectorOf n (elements "0123456789")
A type class for examples.
Defining a spec
describe function combines a list of specs into a larger spec.
Create a set of specifications for a specific type being described. Once you know what you want specs for, use this.
describe "abs" $ do it "returns a positive number given a negative number" $ abs (-1) == 1
A pending example.
If you want to report on a behavior but don't have an example yet, use this.
describe "fancyFormatter" $ do it "can format text in a way that everyone likes" $ pending
You can give an optional reason for why it's pending.
describe "fancyFormatter" $ do it "can format text in a way that everyone likes" $ pending "waiting for clarification from the designers"