test treewide: apply test names best practices

1. test suite names are usually related to the function under tests, not
the whole source or header file
2. test case names should be verbose and describe the high level
behavior

This commits also splits test cases when they are for different
functions, and merges test cases when they are very similar.

Reference:
1. https://github.com/google/googletest/tree/main/googletest/samples
2. https://testing.googleblog.com/2007/02/tott-naming-unit-tests-responsibly.html



Signed-off-by: Nan Zhou <nanzhoumails@gmail.com>
Change-Id: I498cb2076bbaa9f0829f50bca45a2e38a6f4ab7d