Parallel spec execution

You can use parallel to mark specs for parallel execution. This is useful if you want to speed up your tests by utilizing multiple CPUs.

A minimal example

Here is an example:

-- file Spec.hs
import Test.Hspec
import Test.QuickCheck
import Control.Monad

main :: IO ()
main = hspec spec

spec :: Spec
spec = parallel $ do
  describe "expensiveOperation" $ do
    replicateM_ 4 $ do
      it "is expensive" $ do
        property expensiveOperation

expensiveOperation :: [[String]] -> Bool
expensiveOperation xs = (concat . concat) xs == (concat . concat) xs

Link the program with -threaded and pass +RTS -N -RTS when running it:

ghc -threaded Spec.hs

./Spec +RTS -N -RTS

All specs that are not explicitly marked with parallel are run in the application's main thread.

By default, the number of threads available for parallel execution is equal to the number of processors available to the process, as determined by +RTS -N. A different number (higher or lower) can be specified with Hspec's -j option. Note that this number is in addition to the main thread.

Running all tests in parallel with `hspec-discover`

If you are using hspec-discover to generate a test driver then you can use a spec hook to apply parallel to all spec items:

-- test/SpecHook.hs
module SpecHook where

import Test.Hspec

hook :: Spec -> Spec
hook = parallel