Add test case for leaf span.

apm-sniffer/apm-agent-core/src/test/java/org/skywalking/apm/agent/core/context/LeafSpanTestCase.java

+package org.skywalking.apm.agent.core.context;
+
+import java.util.Map;
+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * @author wusheng
+ */
+public class LeafSpanTestCase {
+    @Test
+    public void testLeaf() {
+        LeafSpan span = new LeafSpan(0, "serviceA", System.currentTimeMillis());
+        span.push();
+        span.setOperationName("serviceA2");
+        span.setTag("key", "value-text");
+        span.setTag("key2", false);
+        span.setTag("key3", 1);
+
+        //start 2nd span
+        span.push();
+
+        Assert.assertFalse(span.isFinished());
+        Assert.assertTrue(span.isLeaf());
+        span.setOperationName("service123");
+        span.setTag("key", "value-text2");
+        span.setTag("key2", true);
+        span.setTag("key3", 2);
+        Assert.assertEquals("serviceA2", span.getOperationName());
+        Assert.assertEquals("value-text", span.getStrTag("key"));
+        Assert.assertFalse(span.getBoolTag("key2"));
+        Assert.assertEquals(1, span.getIntTag("key3").intValue());
+
+        //end 2nd span
+        span.pop();
+
+        span.pop();
+        Assert.assertTrue(span.isFinished());
+    }
+}