这里的do well on与其后的名词test有关，因为名词test前可以搭配介词in和on。如：

She got a grade of seventy-nine on (in) the test.  测验她得了79分。

He tried his hardest on (in) the test.  他在考试中尽了最大的努力。

The class’s poor performance on (in) the test horrified the teacher.  这个班的考试成绩之差让老师感到震惊。

又如下面两句也是用do well on，也与其后的介词oral, examination有关：

I did well on the oral but not on the written paper. 我口试考得好，但笔试不怎么样。

Our professor observed that we all did well on the examination.  我们的教授说我们考试成绩都很好。