test: Improve test environment setup and error handling/reporting

During test setup, we used to call a vimscript function(BeforeEachTest) that
attempted to restore Nvim to it's initial state as much as possible in order to
provide a clean environment for running new tests. This approach has proven to
be unreliable, as some tests leave state that can affect other tests, eventually
causing failures that are difficult to debug.

This commit changes the 'clear' function so it will restart Nvim every time it
is called, which is a slower, but more reliable solution that will simplify
spotting bugs in the future.

Some other improvements/fixes were also performed:

- Whenever an error is detected in a handler passed to "run()", the event loop
  will be stopped and the error will be propagated to the main thread.
- Errors and the "cleanup()" function will always send a quit command to the
  current Nvim instance. This should prevent memory starvation when running
  tests under valgrind(where each Nvim instance can consume a lot of memory).
- Fixed a wrong assertion in server_requests_spec.lua. Previously the failure
  was undetected in a notification handler.
- Fixed some tests to expect fully clean registers. The deleted cleanup function
  used to put an empty string in every register, but that resulted in a extra
  line being added.

test/functional/api/server_requests_spec.lua

@@ -4,7 +4,6 @@
 local helpers = require('test.functional.helpers')
 local clear, nvim, eval = helpers.clear, helpers.nvim, helpers.eval
 local eq, run, stop = helpers.eq, helpers.run, helpers.stop
-local restart = helpers.restart
 
 
 
@@ -15,7 +14,6 @@ describe('server -> client', function()
     clear()
     cid = nvim('get_api_info')[1]
   end)
-  teardown(restart)
 
   describe('simple call', function()
     it('works', function()
@@ -110,7 +108,7 @@ describe('server -> client', function()
           return
         end
         notified = notified + 1
-        eq('notified', eval('rpcrequest('..cid..', "notify")'))
+        eq('notified!', eval('rpcrequest('..cid..', "notify")'))
       end
 
       run(on_request, on_notification, on_setup)

test/functional/helpers.lua

@@ -1,10 +1,11 @@
+require('coxpcall')
 local Loop = require('nvim.loop')
 local MsgpackStream = require('nvim.msgpack_stream')
 local AsyncSession = require('nvim.async_session')
 local Session = require('nvim.session')
 
 local nvim_prog = os.getenv('NVIM_PROG') or 'build/bin/nvim'
-local nvim_argv = {nvim_prog, '-u', 'NONE', '-N', '--embed'}
+local nvim_argv = {nvim_prog, '-u', 'NONE', '-i', 'NONE', '-N', '--embed'}
 
 if os.getenv('VALGRIND') then
   local log_file = os.getenv('VALGRIND_LOG') or 'valgrind-%p.log'
@@ -23,74 +24,7 @@ if os.getenv('VALGRIND') then
   nvim_argv = valgrind_argv
 end
 
-local session
-
-local rawfeed
-local function restart()
-  local loop = Loop.new()
-  local msgpack_stream = MsgpackStream.new(loop)
-  local async_session = AsyncSession.new(msgpack_stream)
-  session = Session.new(async_session)
-  loop:spawn(nvim_argv)
-  rawfeed([[:function BeforeEachTest()
-    set all&
-    redir => groups
-    silent augroup
-    redir END
-    for group in split(groups)
-      exe 'augroup '.group
-      autocmd!
-      augroup END
-    endfor
-    autocmd!
-    tabnew
-    let curbufnum = eval(bufnr('%'))
-    redir => buflist
-    silent ls!
-    redir END
-    let bufnums = []
-    for buf in split(buflist, '\n')
-      let bufnum = eval(split(buf, '[ u]')[0])
-      if bufnum != curbufnum
-        call add(bufnums, bufnum)
-      endif
-    endfor
-    if len(bufnums) > 0
-      exe 'silent bwipeout! '.join(bufnums, ' ')
-    endif
-    silent tabonly
-    for k in keys(g:)
-      exe 'unlet g:'.k
-    endfor
-    filetype plugin indent off
-    mapclear
-    mapclear!
-    abclear
-    comclear
-    let regs = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789/-"'
-    let i = 0
-    while i < strlen(regs)
-      call setreg(regs[i], '')
-      let i = i+1
-    endwhile
-    redir => funcs
-    silent! function
-    redir END
-    for fname in split(funcs, '\n')
-      let matches = matchlist(fname, '\v^function ([^()<>]+)')
-      if type([]) == type(matches) && matches[1] !~ 'BeforeEachTest'
-        exe 'silent! delfunc '.matches[1]
-      endif
-    endfor
-    let options = ['shell', 'fileignorecase']
-    for option in options
-      exe 'set '.option.'&'
-    endfor
-  endfunction
-  ]])
-end
-
-local loop_running, last_error
+local session, loop_running, last_error
 
 local function request(method, ...)
   local status, rv = session:request(method, ...)
@@ -112,9 +46,32 @@ local function next_message()
   return session:next_message()
 end
 
+local function call_and_stop_on_error(...)
+  local status, result = copcall(...)
+  if not status then
+    session:stop()
+    last_error = result
+    return ''
+  end
+  return result
+end
+
 local function run(request_cb, notification_cb, setup_cb)
+
+  local function on_request(method, args)
+    return call_and_stop_on_error(request_cb, method, args)
+  end
+
+  local function on_notification(method, args)
+    call_and_stop_on_error(notification_cb, method, args)
+  end
+
+  local function on_setup()
+    call_and_stop_on_error(setup_cb)
+  end
+
   loop_running = true
-  session:run(request_cb, notification_cb, setup_cb)
+  session:run(on_request, on_notification, on_setup)
   loop_running = false
   if last_error then
     local err = last_error
@@ -153,7 +110,7 @@ local function buffer_slice(start, stop, buffer_idx)
 end
 
 local function nvim_replace_termcodes(input)
-  return request('vim_replace_termcodes', input, false, true, true )
+  return request('vim_replace_termcodes', input, false, true, true)
 end
 
 local function dedent(str)
@@ -178,22 +135,29 @@ local function dedent(str)
   return str
 end
 
-local function clear()
-  nvim_command('call BeforeEachTest()')
-end
-
 local function feed(...)
   for _, v in ipairs({...}) do
     nvim_feed(nvim_replace_termcodes(dedent(v)))
   end
 end
 
-function rawfeed(...)
+local function rawfeed(...)
   for _, v in ipairs({...}) do
     nvim_feed(dedent(v), 'nt')
   end
 end
 
+local function clear()
+  if session then
+    session:request('vim_command', 'qa!')
+  end
+  local loop = Loop.new()
+  local msgpack_stream = MsgpackStream.new(loop)
+  local async_session = AsyncSession.new(msgpack_stream)
+  session = Session.new(async_session)
+  loop:spawn(nvim_argv)
+end
+
 local function insert(...)
   nvim_feed('i', 'nt')
   rawfeed(...)
@@ -271,12 +235,11 @@ local function curtab(method, ...)
   return tabpage(method, tab, ...)
 end
 
-restart()
+clear()
 
 return {
   clear = clear,
   dedent = dedent,
-  restart = restart,
   rawfeed = rawfeed,
   insert = insert,
   feed = feed,

test/functional/legacy/006_argument_list_spec.lua

@@ -50,7 +50,7 @@ describe('argument list', function()
 
     execute('%d')
     execute('0put=@a')
-    execute('1d | $d')
+    execute('$d')
 
     eq(dedent([[
       start of test file Xxx1

test/functional/legacy/007_ball_buffer_list_spec.lua

@@ -51,7 +51,7 @@ describe(':ball', function()
     execute('bf')
     execute('%d')
     execute('0put=@a')
-    execute('1d | $d')
+    execute('$d')
 
     expect([[
       start of test file Xxx4

test/functional/legacy/021_control_wi_spec.lua

@@ -31,7 +31,7 @@ describe('CTRL-W CTRL-I', function()
 
     -- Clean buffer and put register
     feed('ggdG"ap')
-    execute('1,2d')
+    execute('1d')
 
     -- The buffer should now contain:
     expect([[

test/functional/legacy/023_edit_arguments_spec.lua

@@ -35,8 +35,8 @@ describe(':edit', function()
     execute('%d')
     execute('0put a')
 
-    -- Remove empty lines
-    execute('1d | $d')
+    -- Remove empty line
+    execute('$d')
 
     -- The buffer should now contain
     expect([[

test/functional/legacy/041_writing_and_reading_hundred_kbyte_spec.lua

@@ -25,7 +25,7 @@ describe('writing and reading a file of over 100 Kbyte', function()
     execute('6005yank A')
     execute('%d')
     execute('0put a')
-    execute('1d | $d')
+    execute('$d')
     execute('w!')
 
     expect([[

test/functional/legacy/options_spec.lua

@@ -2,11 +2,10 @@
 -- other tests, so restart nvim in the teardown hook
 
 local helpers = require('test.functional.helpers')
-local restart, command, clear = helpers.restart, helpers.command, helpers.clear
+local command, clear = helpers.command, helpers.clear
 
 describe('options', function()
   setup(clear)
-  teardown(restart)
 
   it('is working', function()
     command('options')