bug fixed for getHoldable UnsupoortedOperationException

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

@@ -0,0 +1,45 @@
+package com.alibaba.druid.bvt.pool;
+
+import java.sql.Connection;
+import java.sql.SQLException;
+
+import junit.framework.TestCase;
+
+import com.alibaba.druid.filter.Filter;
+import com.alibaba.druid.filter.FilterAdapter;
+import com.alibaba.druid.filter.FilterChain;
+import com.alibaba.druid.pool.DruidDataSource;
+import com.alibaba.druid.proxy.jdbc.ConnectionProxy;
+
+
+public class HoldableUnsupportTest extends TestCase {
+    private DruidDataSource dataSource;
+
+    protected void setUp() throws Exception {
+        dataSource = new DruidDataSource();
+        dataSource.setUrl("jdbc:mock:xxx");
+        Filter filter = new FilterAdapter() {
+            @Override
+            public int connection_getHoldability(FilterChain chain, ConnectionProxy connection) throws SQLException {
+                throw new UnsupportedOperationException();
+            }
+        };
+        dataSource.getProxyFilters().add(filter);
+
+    }
+
+    protected void tearDown() throws Exception {
+        dataSource.close();
+    }
+    
+    public void test_0 () throws Exception {
+        Connection[] connections = new Connection[8];
+        for (int i = 0; i < connections.length; ++i) {
+            connections[i] = dataSource.getConnection();
+        }
+        
+        for (int i = 0; i < connections.length; ++i) {
+            connections[i].close();
+        }
+    }
+}