Hope this will make people using feed_command less likely: this hides bugs.
Already found at least two:
1. msgpackparse() will show internal error: hash_add() in case of duplicate
keys, though it will still work correctly. Currently silenced.
2. ttimeoutlen was spelled incorrectly, resulting in option not being set when
expected. Test was still functioning somehow though. Currently fixed.
It is otherwise impossible to determine which test failed sanitizer/valgrind
check. test/functional/helpers.lua module return was changed so that tests which
do not provide after_each function to get new check will automatically fail.
Some parts of the test depend on gzip(1). They are skipped if gzip is not
available.
Some `:write` and `:edit` commands produce messages and "hit enter" prompts
that had to be treated with an extra `feed('<C-L>')`. In the original test
file this was not neccessary because it was `:source!`ed.
