Move tests from ManageDocks to tests/

The change to use a newtype for RectC is kind of ugly, but this way instances
are less likely to conflict in the tests.

tests/ManageDocks.hs

@@ -0,0 +1,21 @@
+module ManageDocks where
+import XMonad
+import XMonad.Hooks.ManageDocks
+import Test.QuickCheck
+import Foreign.C.Types
+import Properties
+
+instance Arbitrary CLong where
+    arbitrary = fromIntegral `fmap` (arbitrary :: Gen Int)
+instance Arbitrary RectC where
+    arbitrary = do
+        (x,y) <- arbitrary
+        NonNegative w <- arbitrary
+        NonNegative h <- arbitrary
+        return $ RectC (x,y,x+w,y+h)
+
+prop_r2c_c2r :: RectC -> Bool
+prop_r2c_c2r r = r2c (c2r r) == r
+
+prop_c2r_r2c :: Rectangle -> Bool
+prop_c2r_r2c r = c2r (r2c r) == r