pretty report inequality

ExpressiveShouldBe.hs

{-
dependencies:
- base 
- protolude
- tree-diff
-}

import Data.Typeable (Typeable)
import Data.TreeDiff (toExpr, exprDiff, ansiWlEditExpr, ToExpr)
import Text.Printf (printf)
import Test.HUnit (assertFailure)


-- | show a coloured difference of 2 values
prettyDifferences :: (ToExpr a) => a -> a -> String
prettyDifferences a1 a2 =
  show $ ansiWlEditExpr $ exprDiff (toExpr a1) (toExpr a2)

infixl 4 @?=

-- | equality test which show pretty differences on fail
(@?=) :: (ToExpr a, Eq a, Typeable a) => a -> a -> IO ()
a1 @?= a2 =
  if a1 == a2
    then return ()
    else  assertFailure $ printf "Expected equality:\n%s" $
            prettyDifferences a1 a2

shouldBe :: (ToExpr a, Eq a, Typeable a) => a -> a -> IO ()
shouldBe = (@?=)

*Test.ExpressiveShouldBe 
λ> import Test.HUnit
*Test.ExpressiveShouldBe Test.HUnit 
λ> import GHC.Generics
*Test.ExpressiveShouldBe Test.HUnit GHC.Generics
λ> :set -XDeriveGeneric 
*Test.ExpressiveShouldBe Test.HUnit GHC.Generics
λ> :set -XDeriveAnyClass 
*Test.ExpressiveShouldBe Test.HUnit GHC.Generics
λ> data A = A Int String Char [Int] deriving (Generic, ToExpr, Show, Eq)
*Test.ExpressiveShouldBe Test.HUnit GHC.Generics
λ> runTestTT $ TestList [TestLabel "CVD" $ TestCase $ shouldBe (A 5 "python" 'a' [1,2,3]) (A 2 "haskell" 'a' [1,4,3,5])]
### Failure in: 0:CVD                     
...................
Expected equality:
A -5
  +2
  -"python"
  +"haskell"
  'a'
  [1,-2,+4,3,+5]
Cases: 1  Tried: 1  Errors: 0  Failures: 1