Add test cases to test for as per the PR: #8164

[kavyasrinet]

As per the Axioms and facts mentioned in #8164
We should explicitly check for the following:

• Receiver should block on an empty channel. : Test case to check if receiver blocks on empty channel, and resumes on close. #8166
• Send to a nil channel should block -- As of now, one proposal is to implement a special kind of Unbuffered channel that is a nil channel and check for that.
• Receive from a nil channel blocks
• Closing a nil channel also causes a run-time panic.
• Send to a closed channel panics . (The panic behavior could be : throw an exception or return the false boolean) : Adding panic logic and test case #8171
• Receive from closed channel returns zero value after channel is emptied and otherwise the values in the buffer : Add test case to return zero on a closed channel #8167

[chengduoZH]

@kavyasrinet I am curious about, in Fluid, what's the case with a nil channel?