patch 8.2.0866: not enough tests for buffer writing

Problem:    Not enough tests for buffer writing.
Solution:   Add more tests. Use CheckRunVimInTerminal in more places.
            (Yegappan Lakshmanan, closes #6167)

src/testdir/test_writefile.vim

@@ -1,6 +1,7 @@
 " Tests for the writefile() function and some :write commands.
 
 source check.vim
+source term_util.vim
 
 func Test_writefile()
   let f = tempname()
@@ -207,12 +208,6 @@ func Test_saveas()
   close!
   enew | only
   call delete('Xfile')
-
-  call writefile(test_null_list(), 'Xfile')
-  call assert_false(filereadable('Xfile'))
-  call writefile(test_null_blob(), 'Xfile')
-  call assert_false(filereadable('Xfile'))
-  call assert_fails('call writefile([], "")', 'E482:')
 endfunc
 
 func Test_write_errors()
@@ -257,6 +252,138 @@ func Test_write_errors()
   call writefile(test_null_blob(), 'Xfile')
   call assert_false(filereadable('Xfile'))
   call assert_fails('call writefile([], "")', 'E482:')
+
+  " very long file name
+  let long_fname = repeat('n', 5000)
+  call assert_fails('exe "w " .. long_fname', 'E75:')
+  call assert_fails('call writefile([], long_fname)', 'E482:')
+endfunc
+
+" Test for writing to a file which is modified after Vim read it
+func Test_write_file_mtime()
+  CheckEnglish
+  CheckRunVimInTerminal
+
+  " First read the file into a buffer
+  call writefile(["Line1", "Line2"], 'Xfile')
+  let old_ftime = getftime('Xfile')
+  let buf = RunVimInTerminal('Xfile', #{rows : 10})
+  call term_wait(buf)
+  call term_sendkeys(buf, ":set noswapfile\<CR>")
+  call term_wait(buf)
+
+  " Modify the file directly.  Make sure the file modification time is
+  " different. Note that on Linux/Unix, the file is considered modified
+  " outside, only if the difference is 2 seconds or more
+  sleep 1
+  call writefile(["Line3", "Line4"], 'Xfile')
+  let new_ftime = getftime('Xfile')
+  while new_ftime - old_ftime < 2
+    sleep 100m
+    call writefile(["Line3", "Line4"], 'Xfile')
+    let new_ftime = getftime('Xfile')
+  endwhile
+
+  " Try to overwrite the file and check for the prompt
+  call term_sendkeys(buf, ":w\<CR>")
+  call term_wait(buf)
+  call WaitForAssert({-> assert_equal("WARNING: The file has been changed since reading it!!!", term_getline(buf, 9))})
+  call assert_equal("Do you really want to write to it (y/n)?",
+        \ term_getline(buf, 10))
+  call term_sendkeys(buf, "n\<CR>")
+  call term_wait(buf)
+  call assert_equal(new_ftime, getftime('Xfile'))
+  call term_sendkeys(buf, ":w\<CR>")
+  call term_wait(buf)
+  call term_sendkeys(buf, "y\<CR>")
+  call term_wait(buf)
+  call WaitForAssert({-> assert_equal('Line2', readfile('Xfile')[1])})
+
+  " clean up
+  call StopVimInTerminal(buf)
+  call delete('Xfile')
+endfunc
+
+" Test for an autocmd unloading a buffer during a write command
+func Test_write_autocmd_unloadbuf_lockmark()
+  augroup WriteTest
+    autocmd BufWritePre Xfile enew | write
+  augroup END
+  e Xfile
+  call assert_fails('lockmarks write', 'E203:')
+  augroup WriteTest
+    au!
+  augroup END
+  augroup! WriteTest
+endfunc
+
+" Test for writing a buffer with 'acwrite' but without autocmds
+func Test_write_acwrite_error()
+  new Xfile
+  call setline(1, ['line1', 'line2', 'line3'])
+  set buftype=acwrite
+  call assert_fails('write', 'E676:')
+  call assert_fails('1,2write!', 'E676:')
+  call assert_fails('w >>', 'E676:')
+  close!
+endfunc
+
+" Test for adding and removing lines from an autocmd when writing a buffer
+func Test_write_autocmd_add_remove_lines()
+  new Xfile
+  call setline(1, ['aaa', 'bbb', 'ccc', 'ddd'])
+
+  " Autocmd deleting lines from the file when writing a partial file
+  augroup WriteTest2
+    au!
+    autocmd FileWritePre Xfile 1,2d
+  augroup END
+  call assert_fails('2,3w!', 'E204:')
+
+  " Autocmd adding lines to a file when writing a partial file
+  augroup WriteTest2
+    au!
+    autocmd FileWritePre Xfile call append(0, ['xxx', 'yyy'])
+  augroup END
+  %d
+  call setline(1, ['aaa', 'bbb', 'ccc', 'ddd'])
+  1,2w!
+  call assert_equal(['xxx', 'yyy', 'aaa', 'bbb'], readfile('Xfile'))
+
+  " Autocmd deleting lines from the file when writing the whole file
+  augroup WriteTest2
+    au!
+    autocmd BufWritePre Xfile 1,2d
+  augroup END
+  %d
+  call setline(1, ['aaa', 'bbb', 'ccc', 'ddd'])
+  w
+  call assert_equal(['ccc', 'ddd'], readfile('Xfile'))
+
+  augroup WriteTest2
+    au!
+  augroup END
+  augroup! WriteTest2
+
+  close!
+  call delete('Xfile')
+endfunc
+
+" Test for writing to a readonly file
+func Test_write_readonly()
+  " In Cirrus-CI, the freebsd tests are run under a root account. So this test
+  " doesn't fail.
+  CheckNotBSD
+  call writefile([], 'Xfile')
+  call setfperm('Xfile', "r--------")
+  edit Xfile
+  set noreadonly
+  call assert_fails('write', 'E505:')
+  let save_cpo = &cpo
+  set cpo+=W
+  call assert_fails('write!', 'E504:')
+  let &cpo = save_cpo
+  call delete('Xfile')
 endfunc
 
 " vim: shiftwidth=2 sts=2 expandtab