patch 8.1.0144: the :cd command does not have good test coverage

Problem:    The :cd command does not have good test coverage.
Solution:   Add more tests. (Dominique Pelle, closes #2972)

src/testdir/test_cd.vim

@@ -8,6 +8,60 @@ endfunc
func Test_cd_up_and_down()
  let path = getcwd()
  cd ..
  call assert_notequal(path, getcwd())
  exe 'cd ' . path
  call assert_equal(path, getcwd())
endfunc

func Test_cd_no_arg()
  if has('unix')
    " Test that cd without argument goes to $HOME directory on Unix systems.
    let path = getcwd()
    cd
    call assert_equal($HOME, getcwd())
    call assert_notequal(path, getcwd())
    exe 'cd ' . path
    call assert_equal(path, getcwd())
  else
    " Test that cd without argument echoes cwd on non-Unix systems.
    call assert_match(getcwd(), execute('cd'))
  endif
endfunc

func Test_cd_minus()
  " Test the  :cd -  goes back to the previous directory.
  let path = getcwd()
  cd ..
  let path_dotdot = getcwd()
  call assert_notequal(path, path_dotdot)
  cd -
  call assert_equal(path, getcwd())
  cd -
  call assert_equal(path_dotdot, getcwd())
  cd -
  call assert_equal(path, getcwd())
endfunc

func Test_cd_with_cpo_chdir()
  e Xfoo
  call setline(1, 'foo')
  let path = getcwd()
  set cpo+=.

  " :cd should fail when buffer is modified and 'cpo' contains dot.
  call assert_fails('cd ..', 'E747:')
  call assert_equal(path, getcwd())

  " :cd with exclamation mark should succeed.
  cd! ..
  call assert_notequal(path, getcwd())

  " :cd should succeed when buffer has been written.
  w!
  exe 'cd ' . path
  call assert_equal(path, getcwd())

  call delete('Xfoo')
  set cpo&
  bw!
endfunc

src/version.c

@@ -789,6 +789,8 @@ static char *(features[]) =

static int included_patches[] =
{   /* Add new patch number below this line */
/**/
    144,
/**/
    143,
/**/