在使用 so...that... 句式时，若 so... 放在句首，后面可以用倒装。如：

So fast does light travel that it is difficult for us to imagine its speed.

但是，如果没有 that 从句，而单独是 so... 呢，也可以倒装吗？比如：

He didn't dare to go home, so badly had he done in this test.

应该改为下面句子：

As/Because he had done badly in this test, he didn't dare to go home.

一、“so+adj. / adv.”位于句首时的倒装，副词so后接形容词或副词位于句首时，其后用部分倒装：
So cold was the weather that we had to stay at home.
天气太冷，我们只好呆在家里。
So fast does light travel that we can hardly imagine its speed.
光速很快，我们几乎没法想像它的速度。
So sudden was the attack that we had no time to escape.
袭击来得非常突然，我们来不及逃跑。

备注：当such…that…结构的such…置于句首时，such后的句子也要使用部分倒装。

Such a nice man did he seem that we all believe him. 

他像个很和蔼的人，所以我们都喜欢他。

二、“so+助动词+主语”倒装：
当要表示前面提出的某一肯定的情况也同样适合于后者，通常就要用“So+助动词+主语”这种倒装结构：
 You are young and so am I.
你年轻，我也年轻。
She likes music and so do I.
她喜欢音乐，我也喜欢。
 If he can do it, so can I.
要是他能做此事，我也能。

三、(1) 若前面提出某一否定的情况，要表示后者也属于同样的否定情况，则应将其中的so改为neither或nor：
You aren’t young and neither am I.
你不年轻，我也不年轻。
She hasn’t read it and nor have I.
她没有读它，我也没有读。
(2) 注意该结构与表示强调或同意的“so+主语+特殊动词”结构的区别：
"It was cold yesterday." "So it was."
“昨天很冷。”“的确很冷。”
"Father, you promised." "Well, so I did."
“爸爸，你答应过的。”“嗯，是答应过。”

四、so / such...that结构中的so或such位于句首可以构成部分倒装句，表示强调so /such和that之间的部分。

So unreasonable was his price that everybody startled.
他的要价太离谱，令每个人都瞠目结舌。
To such length did she go in rehearsal that the two actors walked out.
她的彩排进行得那么长，以致于那两个演员都走出去了。

He didn't dare to go home, so badly had he done in this test.

先不说倒装问题。你这个句子有误，这应该是一个含有因果关系的主从句，你漏掉了从属连词。应改为：

He didn't dare to go home, because he had done so badly in this test.

或者使用分号，成为两个分句：

He didn't dare to go home；he had done so badly in this test.

就这两个句子而言，是无法倒装的。