refactor: return Either from loadConfig, add Config tests

test/Spec.hs

@@ -3,19 +3,22 @@ module Main (main) where
 import Test.Tasty (defaultMain, testGroup)
 import Test.Tasty.Hspec (testSpec)
 
+import qualified Roux.ConfigSpec
 import qualified Roux.NYTimesSpec
 import qualified Roux.ParserSpec
 import qualified Roux.SchemaOrgSpec
 
 main :: IO ()
 main = do
+    configTests <- testSpec "Config" Roux.ConfigSpec.spec
     parserTests <- testSpec "Parser" Roux.ParserSpec.spec
     nytTests <- testSpec "NYTimes" Roux.NYTimesSpec.spec
     schemaOrgTests <- testSpec "SchemaOrg" Roux.SchemaOrgSpec.spec
     defaultMain $
         testGroup
             "roux-server"
-            [ parserTests
+            [ configTests
+            , parserTests
             , nytTests
             , schemaOrgTests
             ]