Add test for sandbox compatibility with ghc < 7.8

test/GhcPkgSpec.hs

@@ -1,6 +1,8 @@
+{-# LANGUAGE CPP #-}
 module GhcPkgSpec where
 
 import Language.Haskell.GhcMod.GhcPkg
+import Language.Haskell.GhcMod.Types
 
 import System.Directory
 import System.FilePath ((</>))
@@ -9,6 +11,13 @@ import Test.Hspec
 spec :: Spec
 spec = do
     describe "getSandboxDb" $ do
+-- ghc < 7.8
+#if !MIN_VERSION_ghc(7,8,0)
+        it "does include a sandbox with ghc < 7.8" $ do
+            cwd <- getCurrentDirectory
+            getPackageDbStack "test/data/" `shouldReturn` [GlobalDb, PackageDb $ cwd </> "test/data/.cabal-sandbox/i386-osx-ghc-7.6.3-packages.conf.d"]
+#endif
+
         it "parses a config file and extracts sandbox package db" $ do
             cwd <- getCurrentDirectory
             pkgDb <- getSandboxDb "test/data/"