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 textual descriptions of behavior and examples for that behavior. The examples serve as test cases for the specified behavior. Hspec's mechanism for examples is extensible. Support for QuickCheck properties and HUnit tests is included in the core package.
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
Create a spec item.
A spec item consists of:
- a textual description of a desired behavior
- an example for that behavior
describe "absolute" $ do it "returns a positive number when given a negative number" $ absolute (-1) == 1
A pending example.
If you want to textually specify a behavior but do not 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"