A fork of hspec-expectations where:
shouldBe
shows a diff, colored with hscolour and pretty-printed with nicify. That works for all types that haveShow
instances that produce valid Haskell code. Which is most instances really. Definitely the derived ones.
(inspired by ScalaTest's ShouldMatchers)
The three main primitives are shouldBe
, shouldSatisfy
and
shouldThrow
. They can be used with
HUnit, or any framework that
integrates with HUnit, like
test-framework or
Hspec.
Here is an example that uses Hspec. It's a partial specification of itself.
import Test.Hspec
import Control.Exception
main :: IO ()
main = hspec $ do
describe "shouldBe" $ do
it "asserts equality" $ do
"foo" `shouldBe` "foo"
describe "shouldSatisfy" $ do
it "asserts that a predicate holds" $ do
"bar" `shouldSatisfy` (not . null)
describe "shouldThrow" $ do
it "asserts that an exception is thrown" $ do
evaluate (1 `div` 0 :: Int) `shouldThrow` (== DivideByZero)
shouldBe
is just an alias for HUnit's @?=
.
shouldSatisfy
asserts that some predicate holds for a given value.
"bar" `shouldSatisfy` (not . null)
It is similar to HUnit's assertBool
, but gives a useful error message.
>>> 23 `shouldSatisfy` (> 42)
*** Exception: HUnitFailure "23 did not satisfy predicate!"
shouldReturn
asserts that an action returns a given value.
launchMissiles `shouldReturn` Left "permission error"
shouldThrow
asserts that an exception is thrown. The precise nature of
that exception is described with a Selector
.
error "foobar" `shouldThrow` anyException
A Selector
is a predicate, it can simultaneously constrain the type
and value of an exception.
throw DivideByZero `shouldThrow` (== DivideByZero)
To select all exceptions of a given type, const True
can be used.
error "foobar" `shouldThrow` (const True :: Selector ErrorCall)
For convenience, predefined selectors for some standard exceptions are provided.
error "foobar" `shouldThrow` anyErrorCall
Some exceptions (like ErrorCall
) have no Eq
instance, so checking
for a specific value requires pattern matching.
error "foobar" `shouldThrow` (\e -> case e of
ErrorCall "foobar" -> True
_ -> False
)
For such exceptions, combinators that construct selectors are provided. Each combinator corresponds to a constructor; it takes the same arguments, and has the same name (but starting with a lower-case letter).
error "foobar" `shouldThrow` errorCall "foobar"