add testcase & bug fixed for executeQuery return null

src/test/java/com/alibaba/druid/bvt/pool/TransactionTest.java

@@ -0,0 +1,35 @@
+package com.alibaba.druid.bvt.pool;
+
+import java.sql.Connection;
+import java.sql.PreparedStatement;
+
+import junit.framework.TestCase;
+
+import com.alibaba.druid.pool.DruidDataSource;
+
+public class TransactionTest extends TestCase {
+    private DruidDataSource dataSource;
+
+    protected void setUp() throws Exception {
+        dataSource = new DruidDataSource();
+        dataSource.setUrl("jdbc:mock:xxx");
+        dataSource.setTestOnBorrow(false);
+    }
+
+    protected void tearDown() throws Exception {
+        dataSource.close();
+    }
+    
+    public void test_txn() throws Exception {
+        Connection conn = dataSource.getConnection();
+        
+        conn.setAutoCommit(false);
+        for (int i = 0; i < 100; ++i) {
+            PreparedStatement stmt = conn.prepareStatement("select + " + (i % 10));
+            stmt.executeUpdate();
+            stmt.close();
+        }
+        conn.commit();
+        conn.close();
+    }
+}