Add simple tests for DictionaryUtil. (apache#3301)

apm-sniffer/apm-agent-core/src/test/java/org/apache/skywalking/apm/agent/core/dictionary/DictionaryUtilTests.java

@@ -0,0 +1,39 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package org.apache.skywalking.apm.agent.core.dictionary;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * @author Alan Lau
+ */
+public class DictionaryUtilTests {
+
+    @Test
+    public void testNullValue() {
+        Assert.assertEquals(0, DictionaryUtil.nullValue());
+    }
+
+    @Test
+    public void testIsNull() {
+        Assert.assertEquals(false, DictionaryUtil.isNull(1));
+        Assert.assertEquals(true, DictionaryUtil.isNull(0));
+    }
+}