vim-patch:8.2.0982: insufficient testing for reading/writing files

Problem:    Insufficient testing for reading/writing files.
Solution:   Add more tests. (Yegappan Lakshmanan, closes vim/vim#6257)
            Add "ui_delay" to test_override() and use it for the CTRL-O test.
b340baed9f

Omit test_override().
Reorder test_writefile.vim to match Vim.

test/functional/legacy/filechanged_spec.lua

@@ -67,6 +67,15 @@ describe('file changed dialog', function()
         call assert_equal(1, line('$'))
         call assert_equal('new line', getline(1))
 
+        " File created after starting to edit it
+        call delete('Xchanged_d')
+        new Xchanged_d
+        call writefile(['one'], 'Xchanged_d')
+        call nvim_input('L')
+        checktime Xchanged_d
+        call assert_equal(['one'], getline(1, '$'))
+        close!
+
         bwipe!
         call delete('Xchanged_d')
       endfunc