Add remaining haskell book exercises

Haskell-book/14/morse/tests/WordNumberTest.hs

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+module Main where
+
+import Test.Hspec
+import WordNumber (digitToWord, digits, wordNumber)
+
+main :: IO ()
+main = hspec $ do
+    describe "digitToWord" $ do
+        it "returns zero for 0" $ do
+            digitToWord 0 `shouldBe`"zero"
+        it "returns one for 1" $ do
+            digitToWord 1 `shouldBe` "one"
+
+    describe "digits" $ do
+        it "returns [1] for 1" $ do
+            digits 1 `shouldBe` [1]
+        it "returns [1, 0, 0] for 100" $ do
+            digits 100 `shouldBe` [1, 0, 0]
+
+    describe "wordNumber" $ do
+        it "one-zero-zero given 100" $ do
+            wordNumber 100 `shouldBe` "one-zero-zero"
+        it "nine-zero-zero-one for 9001" $ do
+            wordNumber 9001 `shouldBe` "nine-zero-zero-one"