add slf4j logging testcase

src/main/java/com/alibaba/druid/wall/WallFilter.java

@@ -23,7 +23,6 @@ import java.util.List;
 import java.util.Map;
 import java.util.Set;
 
-import com.alibaba.druid.DruidRuntimeException;
 import com.alibaba.druid.filter.FilterAdapter;
 import com.alibaba.druid.filter.FilterChain;
 import com.alibaba.druid.proxy.jdbc.CallableStatementProxy;
@@ -159,12 +158,6 @@ public class WallFilter extends FilterAdapter implements WallFilterMBean {
         return inited;
     }
 
-    public void checkInit() {
-        if (inited) {
-            throw new DruidRuntimeException("wall filter is inited");
-        }
-    }
-
     @Override
     public void statement_addBatch(FilterChain chain, StatementProxy statement, String sql) throws SQLException {
         createWallContext(statement);

src/test/java/com/alibaba/druid/bvt/support/logging/SLF4JImplTest.java

@@ -0,0 +1,24 @@
+package com.alibaba.druid.bvt.support.logging;
+
+import junit.framework.TestCase;
+
+import com.alibaba.druid.pool.DruidDataSource;
+import com.alibaba.druid.support.logging.SLF4JImpl;
+
+public class SLF4JImplTest extends TestCase {
+
+    public void test_0() throws Exception {
+        SLF4JImpl impl = new SLF4JImpl(DruidDataSource.class.getName());
+       
+        impl.isDebugEnabled();
+        impl.isInfoEnabled();
+        impl.isWarnEnabled();
+        impl.debug("");
+        impl.debug("", new Exception());
+        impl.info("");
+        impl.warn("");
+        impl.warn("", new Exception());
+        impl.error("");
+        impl.error("", new Exception());
+    }
+}