etcdserver tests: test dir=true and prevExist=true

Test that if dir=true and prevExist=true PUT only if the target node is a
directory. Otherwise return "Not a directory".
Addresses issue etcd-io#518 on github

etcdserver/server_test.go

@@ -30,6 +30,7 @@ import (
 	"time"
 
 	"github.com/coreos/etcd/Godeps/_workspace/src/golang.org/x/net/context"
+	etcdErr "github.com/coreos/etcd/error"
 	pb "github.com/coreos/etcd/etcdserver/etcdserverpb"
 	"github.com/coreos/etcd/pkg/idutil"
 	"github.com/coreos/etcd/pkg/pbutil"
@@ -294,6 +295,17 @@ func TestApplyRequest(t *testing.T) {
 				},
 			},
 		},
+		// PUT with PrevExist and Dir both true ==> IsKeyDir
+		{
+			pb.Request{Method: "PUT", ID: 1, Dir: true, PrevExist: pbutil.Boolp(true)},
+			Response{err: etcdErr.NewError(etcdErr.EcodeNotDir, "", 0)},
+			[]testutil.Action{
+				{
+					Name:   "IsKeyDir",
+					Params: []interface{}{""},
+				},
+			},
+		},
 		// DELETE ==> Delete
 		{
 			pb.Request{Method: "DELETE", ID: 1},
@@ -1151,6 +1163,13 @@ type storeRecorder struct{ testutil.Recorder }
 
 func (s *storeRecorder) Version() int  { return 0 }
 func (s *storeRecorder) Index() uint64 { return 0 }
+func (s *storeRecorder) IsKeyDir(nodePath string) bool {
+	s.Record(testutil.Action{
+		Name:   "IsKeyDir",
+		Params: []interface{}{nodePath},
+	})
+	return false
+}
 func (s *storeRecorder) Get(path string, recursive, sorted bool) (*store.Event, error) {
 	s.Record(testutil.Action{
 		Name:   "Get",