- I knew that class test would be held at 11:00 AM.
- I knew that there was class test at 11:00 AM.
What are the differences between them? Do they mean same meaning?
(Firstly - class test requires an article: the definite article, "the"; or the indefinite article, "a".)
I knew that the class test would be held at 11:00 AM.
This is in essence a statement of what you believed in the past. In the past, you believed that, at a moment which was then in the future but which is now in the past, a class test was going to be held.
I knew that there was [going to be] a class test at 11:00 AM.
Back in the past I was certain either that a class test was happening at that same time, or that a class test had already happened at an even earlier moment in time
I knew that there would be a class test at 11:00 AM.
I knew, back in the past, that there was going to be a class test in my then future, which is now also the past.
... would is the past tense form of will. Because it is a past tense it is used:
to talk about the past.
to talk about hypotheses – things that are imagined rather than true.