Add basic testing infrastructure

What sort of tests we'll be able to add is yet to be figured out, but
this at least puts a no-op, hspec-based testing target in place.

test/Spec.hs

@@ -0,0 +1 @@
+{-# OPTIONS_GHC -F -pgmF hspec-discover #-}

test/Yesod/Auth/OAuth2Spec.hs

@@ -0,0 +1,15 @@
+module Yesod.Auth.OAuth2Spec
+    ( main
+    , spec
+    ) where
+
+import Test.Hspec
+import Yesod.Auth.OAuth2
+
+main :: IO ()
+main = hspec spec
+
+spec :: Spec
+spec = describe "authOAuth2" $
+    it "works" $
+        True `shouldBe` True

yesod-auth-oauth2.cabal

@@ -50,6 +50,15 @@ library
 
     ghc-options:     -Wall
 
+test-suite test
+  type:              exitcode-stdio-1.0
+  main-is:           Spec.hs
+  hs-source-dirs:    test
+  ghc-options:       -Wall
+  build-depends:   base
+                 , yesod-auth-oauth2
+                 , hspec
+
 source-repository head
   type:     git
   location: https://github.com/thoughtbot/yesod-auth-oauth2.git