I can't help you with the Chinese part, but you can explain in other words what the two tenses mean. Let me change the sentence a little to make it easier to understand. "I've been too busy to get ready, so I didn't take the test yesterday." This sentence means that for the past couple of weeks you have been busy, and you still are busy right now. So, when you had a chance to take the test yesterday, you couldn't. If they were to offer for you to take the test tomorrow, you still wouldn't take it, because you "have been too busy to get ready," and that implies that up to this very moment you have been too busy to get ready. "I had been too busy to get ready, so I didn't take the test yesterday." This one means that in the week or two before yesterday's scheduled test, you just didn't have time to get ready for it. So, yesterday you didn't take it. Today maybe you have loads of time; you haven't told us anything about today. Maybe you will study a lot today and take it tomorrow when they offer to give you the test again. The first example is in the present perfect tense. "I have been too busy..." That means that starting in the past and all the way up to right now, you have been too busy. The second example is in the past perfect tense. " I had been too busy to get ready..." That one means that in the time BEFORE a certain point in the past (and that point in the past is yesterday when they offered to give you the test) you didn't have time to study. It means that in the week or two before yesterday, when the test was offered, you did not have time to study for it. Maybe today you have tons of time, and you will take the test tomorrow.

" I have been too busy to have enough practice, so I did'nt take the test" 我（到现在都）一直很忙，没有足够的练习，所以没有参加（昨天）的考试。 " I had been too busy to have enough practice, so I did'nt take the test". 我（过去）一直很忙，没有足够的练习，所以没有参加（昨天）的考试。

have been 是现在完成时，表示动作或者状态一直持续到现在，或者对现在产生影响；had been是过去完成时，表示在过去的某个时间段的状态，对现在没有影响。