Show how to rerun individual spec items on test failures (close #205)

CHANGES.markdown

@@ -1,3 +1,6 @@
+## Changes in 2.5.4
+  - Show how to rerun individual spec items on test failures (see #205)
+
 ## Changes in 2.5.3
   - Treat character escapes like `\NUL` as single tokens on `--diff` (see #351)
   - Allow a `/` at the beginning and at the end of an absolute path that is

hspec-core/src/Test/Hspec/Core/Formatters.hs

@@ -230,6 +230,9 @@ defaultFailedFormatter = do
               (xs, "") -> output xs
               (xs, _ : ys) -> output (xs ++ "\n") >> write (indentation ++ "          ") >> indented output ys
         Error _ e -> withFailColor . indent $ (("uncaught exception: " ++) . formatException) e
+
+      writeLine ""
+      writeLine ("  To rerun use: --match " ++ show (joinPath path))
       where
         indentation = "       "
         indent message = do

hspec-core/src/Test/Hspec/Core/Util.hs

@@ -7,6 +7,7 @@ module Test.Hspec.Core.Util (
 
 -- * Working with paths
 , Path
+, joinPath
 , formatRequirement
 , filterPredicate
 
@@ -67,6 +68,12 @@ lineBreaksAt n input = case words input of
 -- It consists of a list of group descriptions and a requirement description.
 type Path = ([String], String)
 
+-- |
+-- Join a `Path` with slashes.  The result will have a leading and a trailing
+-- slash.
+joinPath :: Path -> String
+joinPath (groups, requirement) = "/" ++ intercalate "/" (groups ++ [requirement]) ++ "/"
+
 -- |
 -- Try to create a proper English sentence from a path by applying some
 -- heuristics.
@@ -83,11 +90,11 @@ formatRequirement (groups, requirement) = groups_ ++ requirement
 
 -- | A predicate that can be used to filter a spec tree.
 filterPredicate :: String -> Path -> Bool
-filterPredicate pattern path@(groups, requirement) =
+filterPredicate pattern path =
      pattern `isInfixOf` plain
   || pattern `isInfixOf` formatted
   where
-    plain = "/" ++ intercalate "/" (groups ++ [requirement]) ++ "/"
+    plain = joinPath path
     formatted = formatRequirement path
 
 -- | The function `formatException` converts an exception to a string.

hspec-core/test/Test/Hspec/Core/FormattersSpec.hs

@@ -217,6 +217,8 @@ spec = do
             , "                 two"
             , "                 third"
             , ""
+            , "  To rerun use: --match \"//\""
+            , ""
 #if __GLASGOW_HASKELL__ == 800
             , "WARNING:"
             , "  Your version of GHC is affected by https://ghc.haskell.org/trac/ghc/ticket/13285."

hspec-core/test/Test/Hspec/Core/RunnerSpec.hs

@@ -199,6 +199,8 @@ spec = do
           , ""
           , "  1) foo"
           , ""
+          , "  To rerun use: --match \"/foo/\""
+          , ""
 #if __GLASGOW_HASKELL__ == 800
           , "WARNING:"
           , "  Your version of GHC is affected by https://ghc.haskell.org/trac/ghc/ticket/13285."
@@ -268,6 +270,8 @@ spec = do
           , ""
           , "  1) bar"
           , ""
+          , "  To rerun use: --match \"/bar/\""
+          , ""
 #if __GLASGOW_HASKELL__ == 800
           , "WARNING:"
           , "  Your version of GHC is affected by https://ghc.haskell.org/trac/ghc/ticket/13285."
@@ -314,6 +318,8 @@ spec = do
           , ""
           , "  1) foo bar"
           , ""
+          , "  To rerun use: --match \"/foo/bar/\""
+          , ""
 #if __GLASGOW_HASKELL__ == 800
           , "WARNING:"
           , "  Your version of GHC is affected by https://ghc.haskell.org/trac/ghc/ticket/13285."