hspec- Behavior Driven Development for Haskell

Safe HaskellNone




NOTE: There is a monadic and a non-monadic API. This is the documentation for the non-monadic API. The monadic API is more stable, so you may prefer it over this one. For documentation on the monadic API look at Test.Hspec.



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.Hspec.QuickCheck
 import Test.Hspec.HUnit ()
 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 number = undefined

 formatPhoneNumber :: String -> String
 formatPhoneNumber number = undefined

The describe function takes a list of behaviors and examples bound together with the it function

 spec = [describe "unformatPhoneNumber" [

A boolean expression can act as a behavior's 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 Test can act as a behavior's example. (must import Test.Hspec.HUnit)

   it "removes the \"ext\" prefix of the extension" $ TestCase $ do
     let expected = "5555551234135"
         actual   = unformatPhoneNumber "(555) 555-1234 ext 135"
     expected @?= actual

An IO() action is treated like an HUnit TestCase. (must import Test.Hspec.HUnit)

   it "converts letters to numbers" $ do
     let expected = "6862377"
         actual   = unformatPhoneNumber "NUMBERS"
     actual @?= expected

The property function allows a QuickCheck property to act as an example. (must import Test.Hspec.QuickCheck)

   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")


data Spec Source

Internal representation of a spec.

type Specs = [Spec]Source

A list of specs.

data Pending Source

A pending example.

Defining a spec

describe :: String -> [Spec] -> SpecSource

The describe function combines a list of specs into a larger spec.

it :: Example a => String -> a -> SpecSource

Create a set of specifications for a specific type being described. Once you know what you want specs for, use this.

 describe "abs" [
   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" [
   it "can format text in a way that everyone likes" $

You can give an optional reason for why it's pending.

 describe "fancyFormatter" [
   it "can format text in a way that everyone likes" $
     pending "waiting for clarification from the designers"

Running a spec

hspec :: Specs -> IO ()Source

Create a document of the given specs and write it to stdout.

Exit the program with exitSuccess if all examples passed, with exitFailure otherwise.

hspecB :: Specs -> IO BoolSource

Create a document of the given specs and write it to stdout.

Return True if all examples passed, False otherwise.

hHspec :: Handle -> Specs -> IO SummarySource

Create a document of the given specs and write it to the given handle.

 writeReport filename specs = withFile filename WriteMode (\h -> hHspec h specs)

data Summary Source

Summary of a test run.




quantify :: Int -> String -> StringSource

Create a more readable display of a quantity of something.


>>> quantify 0 "example"
"0 examples"
>>> quantify 1 "example"
"1 example"
>>> quantify 2 "example"
"2 examples"

data Result Source

The result of running an example.