test(backend): 覆盖注册限流缺省回退

fruitshorts-app-api/src/test/java/com/fruitshorts/app/service/AppAuthServiceTest.java

@@ -204,6 +204,17 @@ class AppAuthServiceTest {
                 .hasMessageContaining("当前网络注册过于频繁");
     }
 
+    @Test
+    void should_fallback_to_default_limit_when_config_is_missing() {
+        given(userMapper.selectCount(any())).willReturn(5L);
+
+        assertThatThrownBy(() -> authService.register(emailRegister("abcd1234", null), "203.0.113.8"))
+                .isInstanceOf(ServiceException.class)
+                .satisfies(ex -> assertThat(((ServiceException) ex).getCode())
+                        .isEqualTo(ErrorCode.TOO_MANY_REQUESTS.getCode()))
+                .hasMessageContaining("当前网络注册过于频繁");
+    }
+
     @Test
     void should_not_limit_by_ip_when_ip_limit_is_zero() {
         stubHappyRegister();