implemented arbitrary rung selection

test/Abacus/App/ActionsSpec.hs

@@ -33,6 +33,7 @@ spec :: Spec
 spec = describe "Actions" $ do
   moveUpSpec
   moveDownSpec
+  selRungSpec
   beadLeftSpec
   beadRightSpec
   rungLeftSpec
@@ -68,6 +69,20 @@ moveDownSpec = describe "moveDown" $ mapM_
     elsewhere = initialState & rungNum .~ 8
     movedDown = initialState & rungNum .~ 1
 
+selRungSpec :: Spec
+selRungSpec = describe "selRung" $ mapM_
+  ( \(desc, rung, expected) -> context desc $
+    it ("should be " ++ show expected) $
+      selRung rung initialState `shouldBe` expected
+  )
+  [ ( "negative rung", -1, initialState )
+  , ( "valid rung",     5, rung5        )
+  , ( "large rung",    11, rung9        )
+  ]
+  where
+    rung5 = initialState & rungNum .~ 5
+    rung9 = initialState & rungNum .~ 9
+
 beadLeftSpec :: Spec
 beadLeftSpec = describe "beadLeft" $ let
   state = initialState