Add simple test of equivalence of unstream variants

It turns out we don't exercise munstream in the test suite at all. (Easy check
is to replace definition with undefined and run test) This is to check
equivalence of all variants.

This is necessary for any changes to unstream machinery. Such as ones that
discussed in haskell#301, haskell#388, haskell#406

vector/tests/Tests/Vector/Boxed.hs

@@ -48,4 +48,5 @@ tests =
     testBoolBoxedVector (undefined :: Data.Vector.Vector Bool)
   , testGroup "Int" $
     testNumericBoxedVector (undefined :: Data.Vector.Vector Int)
+  , testGroup "unstream" $ testUnstream (undefined :: Data.Vector.Vector Int)
   ]

vector/tests/Tests/Vector/Primitive.hs

@@ -37,4 +37,5 @@ tests =
   , testGroup "Double" $
     testNumericPrimitiveVector
       (undefined :: Data.Vector.Primitive.Vector Double)
+  , testGroup "unstream" $ testUnstream (undefined :: Data.Vector.Primitive.Vector Int)
   ]

vector/tests/Tests/Vector/Property.hs

@@ -18,6 +18,7 @@ module Tests.Vector.Property
   , testNumFunctions
   , testNestedVectorFunctions
   , testDataFunctions
+  , testUnstream
   -- re-exports
   , Data
   , Random
@@ -797,3 +798,32 @@ testDataFunctions _ = $(testProperties ['prop_glength])
 
         toA :: Data b => b -> Int
         toA x = maybe (glength x) (const 1) (cast x :: Maybe a)
+
+testUnstream :: forall v. (CommonContext Int v) => v Int -> [TestTree]
+{-# INLINE testUnstream #-}
+testUnstream _ =
+  [ testProperty "unstream == vunstream (exact)" $ \(n :: Int) ->
+      let v1,v2 :: v Int
+          v1 = runST $ V.freeze =<< MV.unstream  (streamExact n)
+          v2 = runST $ V.freeze =<< MV.vunstream (streamExact n)
+      in v1 == v2
+  , testProperty "unstream == vunstream (unknown)" $ \(n :: Int) ->
+      let v1,v2 :: v Int
+          v1 = runST $ V.freeze =<< MV.unstream  (streamUnknown n)
+          v2 = runST $ V.freeze =<< MV.vunstream (streamUnknown n)
+      in v1 == v2
+  --
+  , testProperty "unstreamR ~= vunstream (exact)" $ \(n :: Int) ->
+      let v1,v2 :: v Int
+          v1 = runST $ V.freeze =<< MV.unstreamR (streamExact n)
+          v2 = runST $ V.freeze =<< MV.vunstream (streamExact n)
+      in V.reverse v1 == v2
+  , testProperty "unstreamR ~= vunstream (unknown)" $ \(n :: Int) ->
+      let v1,v2 :: v Int
+          v1 = runST $ V.freeze =<< MV.unstreamR (streamUnknown n)
+          v2 = runST $ V.freeze =<< MV.vunstream (streamUnknown n)
+      in V.reverse v1 == v2
+  ]
+  where
+    streamExact n = S.generate (abs n) id
+    streamUnknown = S.unfoldr (\i -> if i > 0 then (Just (i-1,i-1)) else Nothing) . abs

vector/tests/Tests/Vector/Storable.hs

@@ -36,4 +36,5 @@ tests =
     testNumericStorableVector (undefined :: Data.Vector.Storable.Vector Int)
   , testGroup "Data.Vector.Storable.Vector (Double)" $
     testNumericStorableVector (undefined :: Data.Vector.Storable.Vector Double)
+  , testGroup "unstream" $ testUnstream (undefined :: Data.Vector.Storable.Vector Int)
   ]

vector/tests/Tests/Vector/Unboxed.hs

@@ -66,4 +66,5 @@ tests =
   , testGroup "(Int,Bool,Int)" $
     testTupleUnboxedVector
       (undefined :: Data.Vector.Unboxed.Vector (Int, Bool, Int))
+  , testGroup "unstream" $ testUnstream (undefined :: Data.Vector.Unboxed.Vector Int)
   ]