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,
 /**/