Allow running integration tests only for one language

The --test-arguments can be passed like this:

stack build :integration-test --test-arguments "--language=ruby"

--language is naively parsed right now just to avoid getting in the way
of hspec's option parsing.

semantic-diff.cabal

@@ -193,6 +193,7 @@ test-suite integration-test
                      , hspec >= 2.1.10
                      , hspec-expectations-pretty-diff
                      , semantic-diff
+                     , MissingH
   ghc-options:       -threaded -rtsopts -with-rtsopts=-N -j -pgml=script/g++
   default-language:    Haskell2010
   default-extensions:  DeriveGeneric, FlexibleInstances, OverloadedStrings, NoImplicitPrelude, RecordWildCards

test/SemanticGitDiffSpec.hs

@@ -39,15 +39,18 @@ runTestsIn filePaths format matcher = do
             Left err ->  it ("An error occurred " <> err <> " (" <> filePath <> ")") $ True `shouldBe` False
             Right testCases -> traverse_ (\testCase -> it (testCaseDescription testCase) $ assertDiffSummary testCase format matcher) testCases
 
-spec :: Spec
-spec = parallel $ do
-  diffSummaryFiles <- runIO $ testCaseFiles "test/corpus/diff-summaries"
-  diffSummaryToDoFiles <- runIO $ testCaseFiles "test/corpus/diff-summaries-todo"
-  diffSummaryCrasherFiles <- runIO $ testCaseFiles "test/corpus/diff-summary-crashers"
+spec :: Maybe String -> Spec
+spec maybeLanguage = parallel $ do
+  diffSummaryFiles <- runIO $ testCaseFiles maybeLanguage "test/corpus/diff-summaries"
+  diffSummaryToDoFiles <- runIO $ testCaseFiles maybeLanguage "test/corpus/diff-summaries-todo"
+  diffSummaryCrasherFiles <- runIO $ testCaseFiles maybeLanguage "test/corpus/diff-summary-crashers"
 
   describe "diff summaries" $ runTestsIn diffSummaryFiles Summary shouldBe
   describe "diff summaries todo" $ runTestsIn diffSummaryToDoFiles Summary shouldNotBe
   describe "diff summaries crashers todo" $ runTestsIn diffSummaryCrasherFiles Summary shouldBe
 
-  where testCaseFiles :: String -> IO [FilePath]
-        testCaseFiles = globDir1 (compile "*/*.json")
+  where
+    testCaseFiles :: Maybe String -> String -> IO [FilePath]
+    testCaseFiles maybeLanguage dir = case maybeLanguage of
+      Just language -> globDir1 (compile (language <> "/*.json")) dir
+      Nothing -> globDir1 (compile "*/*.json") dir

test/SpecIntegration.hs

@@ -1,9 +1,24 @@
+{-# LANGUAGE FlexibleContexts #-}
 module Main where
 
 import Prologue
+import Prelude (String)
+import Data.List
+import Data.List.Utils
 import qualified SemanticGitDiffSpec
 import Test.Hspec
+import System.Environment (withArgs)
 
 main :: IO ()
-main = hspec $ parallel $ do
-  describe "DiffSummaries" SemanticGitDiffSpec.spec
+main = do
+  args <- getArgs
+  let (language, rest) = parseCustomArgs args
+  withArgs rest . hspec . parallel $ describe "DiffSummaries" (SemanticGitDiffSpec.spec language)
+  where
+    parseCustomArgs :: [String] -> (Maybe String, [String])
+    parseCustomArgs args = case partitioned of
+      (l:_, rest) -> (toLang l, rest)
+      _ -> (Nothing, args)
+      where
+        partitioned = partition (startswith "--language") args
+        toLang s = Just $ replace "--language=" "" s