题目如下:1. 一个视频广告的插件,设计结构包括Slot, ADSequence, ADInstance三个组成部分 ,设计定义如下:
a. Slot could be consist of multiple ADSequence, and ADSequence could be consist of multiple ADInstance
b. When preload slot, it should preload ADSequence one by one
c. When playback slot, it should play ADSequence one by one
d. When preload the ADSequence, it should preload the ADInstance one by one, only if the previous ADInstance preloading failed should skip it and preload the next one.
e. When playback slot, it should play the ADInstance which has been preloaded
设计test case