This is challenging because there is no network in a unit test and the AJAX call will fail.

这很有挑战性，因为单元测试中没有网络，AJAX调用会失败。

youdao

Testing components that use server resources is a bit challenging, because the components reside in the server context. You can test such a component at the unit level in one of the following ways.

测试使用服务器资源的组件是有挑战性的，因为这些组件存在于这个服务器环境中。

youdao

Fixed-income trading has proved particularly challenging, and he has reorganized the unit's management several times.

FORBES: Beware That Commercial Bank

The investing unit we acquired at the beginning of 2008, so right before all of the particularly challenging period began.

FORBES: Intelligent Investing