Add remaining haskell book exercises

Haskell-book/26/Exercises/test/Spec.hs

@@ -0,0 +1,19 @@
+import Control.Monad.Trans.Reader
+import Exercises
+import Test.Hspec
+
+main :: IO ()
+main = hspec $ do
+    describe "rDec" $ do
+        it "returns a value decremented by one" $ do
+            runReader rDec 1 `shouldBe` 0
+
+        it "decrements all elements of a list" $ do
+            (fmap (runReader rDec) [1..10]) `shouldBe` [0,1,2,3,4,5,6,7,8,9]
+
+    describe "rShow" $ do
+        it "shows a number" $ do
+            runReader rShow 1 `shouldBe` "1"
+
+        it "shows a list" $ do
+            (fmap (runReader rShow) [1..10]) `shouldBe` ["1","2","3","4","5","6","7","8","9","10"]