chore: 增加一个测试用例

litemall-core/src/test/java/org/linlinjava/litemall/core/IntegerTest.java

+package org.linlinjava.litemall.core;
+
+import org.junit.Test;
+
+public class IntegerTest {
+    @Test
+    public void test() {
+        Integer a = new Integer(512);
+        int b = 512;
+        Integer c = new Integer(512);
+        System.out.println(a==b);
+        System.out.println(a.equals(b));
+        System.out.println(a == c);
+        System.out.println(a.equals(c));
+    }
+}