Add unit tests and reimplement FromField

test/Database/PostgreSQL/Opium/FromFieldSpec.hs

@@ -0,0 +1,70 @@
+{-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE OverloadedStrings #-}
+
+module Database.PostgreSQL.Opium.FromFieldSpec (spec) where
+
+import Data.ByteString (ByteString)
+import Data.Text (Text)
+import Database.PostgreSQL.LibPQ (Connection)
+import Database.PostgreSQL.Opium (FromRow)
+import GHC.Generics (Generic)
+import Test.Hspec (SpecWith, describe, it, shouldBe)
+
+import qualified Database.PostgreSQL.Opium as Opium
+
+newtype SingleInt = SingleInt
+  { int :: Int
+  } deriving (Eq, Generic, Show)
+
+instance FromRow SingleInt where
+
+newtype SingleText = SingleText
+  { text :: Text
+  } deriving (Eq, Generic, Show)
+
+instance FromRow SingleText where
+
+newtype SingleString = SingleString
+  { string :: String
+  } deriving (Eq, Generic, Show)
+
+instance FromRow SingleString where
+
+shouldFetch :: (Eq a, FromRow a, Show a) => Connection -> ByteString -> [a] -> IO ()
+shouldFetch conn query expectedRows = do
+  Just actualRows <- Opium.fetch_ conn query
+  actualRows `shouldBe` expectedRows
+
+spec :: SpecWith Connection
+spec = do
+  describe "FromField Int" $ do
+    it "Decodes smallint" $ \conn -> do
+      shouldFetch conn "SELECT 42::SMALLINT AS int" [SingleInt 42]
+
+    it "Decodes integer" $ \conn -> do
+      shouldFetch conn "SELECT 42::INTEGER AS int" [SingleInt 42]
+
+    it "Decodes bigint" $ \conn -> do
+      shouldFetch conn "SELECT 42::BIGINT AS int" [SingleInt 42]
+
+  describe "FromField Text" $ do
+    it "Decodes text" $ \conn -> do
+      shouldFetch conn "SELECT 'Hello, World!'::TEXT AS text" [SingleText "Hello, World!"]
+
+    it "Decodes character" $ \conn -> do
+      shouldFetch conn "SELECT 'Hello, World!'::CHARACTER(10) AS text" [SingleText "Hello, Wor"]
+      shouldFetch conn "SELECT 'Hello, World!'::CHARACTER(20) AS text" [SingleText "Hello, World!       "]
+
+    it "Decodes character varying" $ \conn -> do
+      shouldFetch conn "SELECT 'Hello, World!'::CHARACTER VARYING (20) AS text" [SingleText "Hello, World!"]
+
+  describe "FromField String" $ do
+    it "Decodes text" $ \conn -> do
+      shouldFetch conn "SELECT 'Hello, World!'::TEXT AS string" [SingleString "Hello, World!"]
+
+    it "Decodes character" $ \conn -> do
+      shouldFetch conn "SELECT 'Hello, World!'::CHARACTER(10) AS string" [SingleString "Hello, Wor"]
+      shouldFetch conn "SELECT 'Hello, World!'::CHARACTER(20) AS string" [SingleString "Hello, World!       "]
+
+    it "Decodes character varying" $ \conn -> do
+      shouldFetch conn "SELECT 'Hello, World!'::CHARACTER VARYING (20) AS string" [SingleString "Hello, World!"]