Specifically, functions that are run in the context of the test runner
are put in module `test/testutil.lua` while the functions that are run
in the context of the test session are put in
`test/functional/testnvim.lua`.
Closes https://github.com/neovim/neovim/issues/27004.
Problem: Some Normal mode commands not fully tested.
Solution: Add a few more tests. (Yegappan Lakshmanan, closesvim/vim#7073)
d1ad99b654
Cherry-pick test_registers.vim change from patch 8.2.0644.