API: nvim__stats()

Use it to verify fsync() behavior.

test/functional/core/fileio_spec.lua

@@ -3,10 +3,11 @@ local helpers = require('test.functional.helpers')(after_each)
 local clear = helpers.clear
 local command = helpers.command
 local eq = helpers.eq
-local eval = helpers.eval
 local feed = helpers.feed
 local funcs = helpers.funcs
 local nvim_prog = helpers.nvim_prog
+local request = helpers.request
+local retry = helpers.retry
 local rmdir = helpers.rmdir
 local sleep = helpers.sleep
 
@@ -22,20 +23,24 @@ describe('fileio', function()
   end)
 
   it('fsync() codepaths #8304', function()
-    -- This is an "acceptance test" or "smoke test".
-
     clear({ args={ '-i', 'Xtest_startup_shada',
                    '--cmd', 'set directory=Xtest_startup_swapdir' } })
 
     -- These cases ALWAYS force fsync (regardless of 'fsync' option):
 
     -- 1. Idle (CursorHold) with modified buffers (+ 'swapfile').
-    command('set swapfile')
-    command('set updatetime=1')
     command('write Xtest_startup_file1')
     feed('ifoo<esc>h')
-    sleep(2)
-    eq(1, eval('&modified'))
+    command('write')
+    eq(0, request('nvim__stats').fsync)   -- 'nofsync' is the default.
+    command('set swapfile')
+    command('set updatetime=1')
+    feed('izub<esc>h')                    -- File is 'modified'.
+    sleep(3)                              -- Allow 'updatetime' to expire.
+    retry(3, nil, function()
+      eq(1, request('nvim__stats').fsync)
+    end)
+    command('set updatetime=9999')
 
     -- 2. Exit caused by deadly signal (+ 'swapfile').
     local j = funcs.jobstart({ nvim_prog, '-u', 'NONE', '-i',
@@ -51,11 +56,13 @@ describe('fileio', function()
 
     -- 4. Explicit :preserve command.
     command('preserve')
+    eq(2, request('nvim__stats').fsync)
 
     -- 5. Enable 'fsync' option, write file.
     command('set fsync')
     feed('ibaz<esc>h')
     command('write')
+    eq(4, request('nvim__stats').fsync)
   end)
 end)