angular测试用例： 当引用别的自定义组件时且spec.ts 中有truthy方法 报错：is not a known element。。

is not a known element:
1. If 'app-date-picker' is an Angular component, then verify that it is part of this module.
2. If 'app-date-picker' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message. ("
      </nav>
    </div>