Safe Haskell | None |
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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.
Introduction
The three functions you'll use the most are hspec
, describe
, and it
.
Here is an example of functions that format and unformat phone numbers and
the specs for them.
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
The describe
function takes a list of behaviors and examples bound
together with the it
function
spec :: Spec spec = do describe "unformatPhoneNumber" $ do
A Bool
can be used as an example.
it "removes dashes, spaces, and parenthesies" $ unformatPhoneNumber "(555) 555-1234" == "5555551234"
The 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"
An HUnit Assertion
can be used as an example.
it "converts letters to numbers" $ do let expected = "6862377" actual = unformatPhoneNumber "NUMBERS" actual @?= expected
A QuickCheck 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")
Types
A type class for examples.
Setting expectations
module Test.Hspec.Expectations
Defining a spec
describe :: String -> Spec -> SpecSource
The describe
function combines a list of specs into a larger spec.
it :: Example v => String -> v -> SpecSource
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
pending :: String -> PendingSource
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"