Add testcase for merge sort

ghc-events.cabal

@@ -137,3 +137,11 @@ test-suite roundtrip
   hs-source-dirs:   ., test
   build-depends:    ghc-events, base
   extensions:	      RecordWildCards, NamedFieldPuns, BangPatterns, PatternGuards
+
+test-suite merge-sort
+  type:             exitcode-stdio-1.0
+  main-is:          Sort.hs
+  other-modules:    Utils
+  hs-source-dirs:   ., test
+  build-depends:    ghc-events, base, bytestring, filepath, temporary
+  extensions:	      RecordWildCards, NamedFieldPuns, BangPatterns, PatternGuards

test/Sort.hs

@@ -0,0 +1,28 @@
+import Control.Monad
+import System.Exit
+import System.FilePath
+import System.IO.Temp
+
+import GHC.RTS.Events
+import qualified GHC.RTS.Events.Sort as Sort
+import Utils (files, diffLines)
+
+-- | This is chosen to be small to ensure that we tickle the merge sort path.
+sortParams :: Sort.SortParams
+sortParams = Sort.SortParams { chunkSize = 1000, maxFanIn = 10 }
+
+-- | Check that merge sort computes the same result as in-memory sort.
+checkSort :: FilePath -> IO Bool
+checkSort logFile = withSystemTempDirectory "check-sort" $ \tmpDir -> do
+  Right eventlog <- readEventLogFromFile logFile
+  Sort.sortEvents' sortParams tmpDir (tmpDir </> "out") eventlog
+  let inMem = sortEvents $ events $ dat eventlog
+  Right merged <- readEventLogFromFile (tmpDir </> "out")
+  if show (events $ dat merged) == show inMem
+    then return True
+    else putStrLn "bad" >> return False
+
+main :: IO ()
+main = do
+  successes <- mapM checkSort files
+  unless (and successes) exitFailure