add testcase for issue #1990

core/src/test/java/com/alibaba/fastjson2/issues_1900/Issue1990.java

@@ -0,0 +1,30 @@
+package com.alibaba.fastjson2.issues_1900;
+
+import com.alibaba.fastjson2.JSON;
+import com.alibaba.fastjson2.JSONFactory;
+import com.alibaba.fastjson2.PropertyNamingStrategy;
+import com.alibaba.fastjson2.writer.ObjectWriterProvider;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class Issue1990 {
+    @Test
+    public void test() {
+        ObjectWriterProvider provider = JSONFactory.getDefaultObjectWriterProvider();
+
+        PropertyNamingStrategy namingStrategy = provider.getNamingStrategy();
+        try {
+            provider.setNamingStrategy(PropertyNamingStrategy.SnakeCase);
+            Bean bean = new Bean();
+            bean.userId = 123;
+            assertEquals("{\"user_id\":123}", JSON.toJSONString(bean));
+        } finally {
+            provider.setNamingStrategy(namingStrategy);
+        }
+    }
+
+    public static class Bean {
+        public int userId;
+    }
+}