add QC tests for SwapWorkspaces

run with -i..:../tests

tests/test_SwapWorkspaces.hs

@@ -0,0 +1,56 @@
+{-# OPTIONS -fglasgow-exts #-}
+
+import Data.List(find,union)
+import Data.Maybe(fromJust)
+import Test.QuickCheck
+
+import StackSet
+import Properties(T, NonNegative)
+import XMonadContrib.SwapWorkspaces
+
+-- Ensures that no "loss of information" can happen from a swap.
+prop_double_swap (ss :: T) (t1 :: NonNegative Int) (t2 :: NonNegative Int) =
+  t1 `tagMember` ss && t2 `tagMember` ss ==>
+  ss == swap (swap ss)
+  where swap = swapWorkspaces t1 t2
+
+-- Degrade nicely when given invalid data.
+prop_invalid_swap (ss :: T) (t1 :: NonNegative Int) (t2 :: NonNegative Int) =
+  not (t1 `tagMember` ss || t2 `tagMember` ss) ==>
+  ss == swapWorkspaces t1 t2 ss
+
+-- This doesn't pass yet. Probably should.
+-- prop_half_invalid_swap (ss :: T) (t1 :: NonNegative Int) (t2 :: NonNegative Int) =
+--   t1 `tagMember` ss && not (t2 `tagMember` ss) ==>
+--   ss == swapWorkspaces t1 t2 ss
+
+zipWorkspacesWith :: (Workspace i l a -> Workspace i l a -> n) -> StackSet i l a s sd ->
+                     StackSet i l a s sd -> [n]
+zipWorkspacesWith f s t = f (workspace $ current s) (workspace $ current t) :
+                          zipWith f (map workspace $ visible s) (map workspace $ visible t) ++
+                          zipWith f (hidden s)  (hidden t)
+
+-- Swap only modifies the workspaces tagged t1 and t2 -- leaves all others alone.
+prop_swap_only_two (ss :: T) (t1 :: NonNegative Int) (t2 :: NonNegative Int) =
+  t1 `tagMember` ss && t2 `tagMember` ss ==>
+  and $ zipWorkspacesWith mostlyEqual ss (swapWorkspaces t1 t2 ss)
+  where mostlyEqual w1 w2 = map tag [w1, w2] `elem` [[t1, t2], [t2, t1]] || w1 == w2
+
+-- swapWithCurrent stays on current
+prop_swap_with_current (ss :: T) (t :: NonNegative Int) =
+  t `tagMember` ss ==>
+  layout before == layout after && stack before == stack after
+  where before = workspace $ current ss
+        after  = workspace $ current $ swapWithCurrent t ss
+
+main = do
+  putStrLn "Testing double swap"
+  quickCheck prop_double_swap
+  putStrLn "Testing invalid swap"
+  quickCheck prop_invalid_swap
+  -- putStrLn "Testing half-invalid swap"
+  -- quickCheck prop_half_invalid_swap
+  putStrLn "Testing swap only two"
+  quickCheck prop_swap_only_two
+  putStrLn "Testing swap with current"
+  quickCheck prop_swap_with_current