quickcheck duration

Test.hs

@@ -60,6 +60,7 @@ import qualified Utility.Matcher
 import qualified Utility.Exception
 import qualified Utility.Hash
 import qualified Utility.Scheduled
+import qualified Utility.HumanTime
 #ifndef mingw32_HOST_OS
 import qualified GitAnnex
 import qualified Remote.Helper.Encryptable
@@ -140,6 +141,7 @@ quickcheck =
 	, check "prop_parse_show_TrustLog" Logs.Trust.prop_parse_show_TrustLog
 	, check "prop_hashes_stable" Utility.Hash.prop_hashes_stable
 	, check "prop_schedule_roundtrips" Utility.Scheduled.prop_schedule_roundtrips
+	, check "prop_duration_roundtrips" Utility.HumanTime.prop_duration_roundtrips
 	]
   where
 	check desc prop = do

Utility/HumanTime.hs

@@ -10,13 +10,16 @@ module Utility.HumanTime (
 	durationToPOSIXTime,
 	parseDuration,
 	fromDuration,
+	prop_duration_roundtrips
 ) where
 
 import Utility.PartialPrelude
 import Utility.Applicative
+import Utility.QuickCheck
 
 import Data.Time.Clock.POSIX (POSIXTime)
 import Data.Char
+import Control.Applicative
 import qualified Data.Map as M
 
 newtype Duration = Duration { durationSeconds :: Integer }
@@ -37,14 +40,16 @@ parseDuration = Duration <$$> go 0
 		go (n + num * u) rest
 
 fromDuration :: Duration -> String
-fromDuration = concat . map showunit . go [] units . durationSeconds
+fromDuration Duration { durationSeconds = d }
+	| d == 0 = "0s"
+	| otherwise = concat $ map showunit $ go [] units d
   where
 	showunit (u, n)
 		| n > 0 = show n ++ [u]
 		| otherwise = ""
 	go c [] _ = reverse c
-	go c ((u, n):us) d =
-		let (q,r) = d `quotRem` n
+	go c ((u, n):us) v =
+		let (q,r) = v `quotRem` n
 		in go ((u, q):c) us r
 
 units :: [(Char, Integer)]
@@ -70,3 +75,10 @@ hsecs = msecs * 60
 
 msecs :: Integer
 msecs = 60
+
+-- Durations cannot be negative.
+instance Arbitrary Duration where
+	arbitrary = Duration <$> nonNegative arbitrary
+
+prop_duration_roundtrips :: Duration -> Bool
+prop_duration_roundtrips d = parseDuration (fromDuration d) == Just d