Split the code into library and application

tests/SlackBuilder/PackageSpec.hs

@@ -2,7 +2,17 @@ module SlackBuilder.PackageSpec
     ( spec
     ) where 
 
-import Test.Hspec (Spec)
+import SlackBuilder.Package
+import Test.Hspec (Spec, describe, it, shouldBe)
+import Text.URI.QQ (uri)
 
 spec :: Spec
-spec = pure ()
+spec = do
+    describe "renderDownloadWithVersion" $
+        it "renders text as URL" $
+            let given = DownloadTemplate
+                    $ pure
+                    $ StaticPlaceholder "https://example.com"
+                actual = renderDownloadWithVersion given "1.2"
+                expected = Just [uri|https://example.com|]
+             in actual `shouldBe` expected