add testcase for #3579

src/test/java/com/alibaba/json/bvt/issue_3500/Issue3579.java

@@ -0,0 +1,19 @@
+package com.alibaba.json.bvt.issue_3500;
+
+import com.alibaba.fastjson.JSON;
+import com.alibaba.fastjson.serializer.SerializerFeature;
+import junit.framework.TestCase;
+
+import java.math.BigDecimal;
+
+public class Issue3579 extends TestCase {
+    public void test_for_issue() throws Exception {
+        assertEquals("1",
+                JSON.toJSONString(new BigDecimal("1"))
+        );
+
+        assertEquals("1.",
+                JSON.toJSONString(new BigDecimal("1"), SerializerFeature.WriteClassName)
+        );
+    }
+}