add prop for 'differentiate'

darcs-hash:20070927231928-cba2c-84668ba6dab69541e063eaabf57724c13a28a916

1 files changed, 5 insertions, 0 deletions

diff --git a/tests/Properties.hs b/tests/Properties.hs
index aa698bc..0f4b733 100644
--- a/tests/Properties.hs
+++ b/tests/Properties.hs
@@ -538,6 +538,10 @@ prop_screens (x :: T) = n `elem` screens x
  where
     n = current x
 
+prop_differentiate xs =
+        if null xs then differentiate xs == Nothing
+                   else focus (fromJust (differentiate xs)) == head xs
+    where _ = xs :: [Int]
 
 ------------------------------------------------------------------------
 -- some properties for layouts:
@@ -669,6 +673,7 @@ main = do
 
         ,("floating is reversible" , mytest prop_float_reversible)
         ,("screens includes current", mytest prop_screens)
+        ,("differentiate works", mytest prop_differentiate)
 
 {-
         ,("tile 1 window fullsize", mytest prop_tile_fullscreen)