增加驼峰转下划线测试

mybatis-plus-core/src/test/java/com/baomidou/mybatisplus/core/toolkit/StringUtilsTest.java

@@ -0,0 +1,19 @@
+package com.baomidou.mybatisplus.core.toolkit;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+
+/**
+ * @author HCL
+ * Create at 2018/9/17
+ */
+
+public class StringUtilsTest {
+
+    @Test
+    public void camelToUnderlineTest() {
+        String s = "userId";
+        Assert.assertEquals("user_id", StringUtils.camelToUnderline(s));
+    }
+}