Now, then, I ask you this; could I expect--could I believe -could I even remotely imagine--that, feeling as he did, he would do so ungrateful a thing as to add those quite unnecessary fifteen words to his test?--set a trap for me?--expose me as a slanderer of my own town before my own people assembled in a public hall? It was preposterous; it was impossible. His test would contain only the kindly opening clause of my remark. Of that I had no shadow of doubt.

1）His test would contain：为什么要使用would ? 这里的would是过去将来时纯助动词？ 还是情态动词表示推测可能性（或许）呢？

无论是哪种理解，我感觉似乎都不符合故事的背景和上下文。很难理解这里的would含义和用法。

2）of that 如何理解？为什么不是On that ? that具体是指代什么呢？