memfs: fix Stat for directories

* memfs: fix Stat for directories: isDir now returns true for them.

* memfs: fix FileInfo Size for directories.

* test: added further tests for Stat on directories

memfs/memory.go

@@ -78,7 +78,9 @@ func (fs *Memory) Stat(filename string) (billy.FileInfo, error) {
 
 	info, err := fs.ReadDir(fullpath)
 	if err == nil && len(info) != 0 {
-		return newFileInfo(fs.base, fullpath, len(info)+100), nil
+		fi := newFileInfo(fs.base, fullpath, len(info))
+		fi.isDir = true
+		return fi, nil
 	}
 
 	return nil, os.ErrNotExist

test/fs_suite.go

@@ -307,14 +307,22 @@ func (s *FilesystemSuite) TestDirStat(c *C) {
 		c.Assert(f.Close(), IsNil)
 	}
 
+	fi, err := s.Fs.Stat("qux")
+	c.Assert(err, IsNil)
+	c.Assert(fi.Name(), Equals, "qux")
+	c.Assert(fi.IsDir(), Equals, true)
+
 	qux := s.Fs.Dir("qux")
-	fi, err := qux.Stat("baz")
+
+	fi, err = qux.Stat("baz")
 	c.Assert(err, IsNil)
 	c.Assert(fi.Name(), Equals, "baz")
+	c.Assert(fi.IsDir(), Equals, false)
 
 	fi, err = qux.Stat("/baz")
 	c.Assert(err, IsNil)
 	c.Assert(fi.Name(), Equals, "baz")
+	c.Assert(fi.IsDir(), Equals, false)
 }
 
 func (s *FilesystemSuite) TestCreateInDir(c *C) {