diff --git a/ddl/alter_test.go b/ddl/alter_test.go
new file mode 100644
index 0000000000..daa6b5f5ff
--- /dev/null
+++ b/ddl/alter_test.go
@@ -0,0 +1,76 @@
+// Copyright 2015 PingCAP, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package ddl
+
+import (
+	. "github.com/pingcap/check"
+	"github.com/pingcap/tidb/mysql"
+	"github.com/pingcap/tidb/parser/coldef"
+	"github.com/pingcap/tidb/util/types"
+)
+
+func (s *testDDLSuite) TestAlterSpecification(c *C) {
+	tbl := []*AlterSpecification{
+		{
+			Action: AlterTableOpt,
+		},
+		{
+			Action: AlterDropColumn,
+			Name:   "c1",
+		},
+		{Action: AlterDropPrimaryKey},
+		{Action: AlterDropForeignKey,
+			Name: "c"},
+		{Action: AlterDropIndex,
+			Name: "index_c"},
+		{Action: AlterAddConstr,
+			Constraint: nil},
+		{Action: AlterAddConstr,
+			Constraint: &coldef.TableConstraint{
+				Tp: coldef.ConstrPrimaryKey,
+				Keys: []*coldef.IndexColName{
+					{
+						ColumnName: "a",
+						Length:     10,
+					},
+				},
+			}},
+		{Action: AlterAddColumn,
+			Column: &coldef.ColumnDef{
+				Name: "c",
+				Tp:   types.NewFieldType(mysql.TypeLong),
+			},
+			Position: &ColumnPosition{}},
+		{Action: AlterAddColumn,
+			Column: &coldef.ColumnDef{
+				Name: "c",
+				Tp:   types.NewFieldType(mysql.TypeLong),
+			},
+			Position: &ColumnPosition{Type: ColumnPositionFirst}},
+		{Action: AlterAddColumn,
+			Column: &coldef.ColumnDef{
+				Name: "c",
+				Tp:   types.NewFieldType(mysql.TypeLong),
+			},
+			Position: &ColumnPosition{Type: ColumnPositionAfter,
+				RelativeColumn: "c"}},
+
+		// Invalid action returns empty string
+		{Action: -1},
+	}
+
+	for _, spec := range tbl {
+		c.Assert(len(spec.String()), GreaterEqual, 0)
+	}
+}