patch 8.2.1432: various inconsistencies in test files

Problem:    Various inconsistencies in test files.
Solution:   Add modelines where they were missing.  Use Check commands instead
            of silently skipping over tests.  Adjust indents and comments.
            (Ken Takata, closes #6695)
diff --git a/src/testdir/test_cmdline.vim b/src/testdir/test_cmdline.vim
index 539b782..266513e 100644
--- a/src/testdir/test_cmdline.vim
+++ b/src/testdir/test_cmdline.vim
@@ -86,9 +86,7 @@
 endfunc
 
 func Test_map_completion()
-  if !has('cmdline_compl')
-    return
-  endif
+  CheckFeature cmdline_compl
   call feedkeys(":map <unique> <si\<Tab>\<Home>\"\<CR>", 'xt')
   call assert_equal('"map <unique> <silent>', getreg(':'))
   call feedkeys(":map <script> <un\<Tab>\<Home>\"\<CR>", 'xt')
@@ -164,9 +162,7 @@
 endfunc
 
 func Test_match_completion()
-  if !has('cmdline_compl')
-    return
-  endif
+  CheckFeature cmdline_compl
   hi Aardig ctermfg=green
   call feedkeys(":match \<Tab>\<Home>\"\<CR>", 'xt')
   call assert_equal('"match Aardig', getreg(':'))
@@ -175,9 +171,7 @@
 endfunc
 
 func Test_highlight_completion()
-  if !has('cmdline_compl')
-    return
-  endif
+  CheckFeature cmdline_compl
   hi Aardig ctermfg=green
   call feedkeys(":hi \<Tab>\<Home>\"\<CR>", 'xt')
   call assert_equal('"hi Aardig', getreg(':'))
@@ -214,9 +208,7 @@
 endfunc
 
 func Test_getcompletion()
-  if !has('cmdline_compl')
-    return
-  endif
+  CheckFeature cmdline_compl
   let groupcount = len(getcompletion('', 'event'))
   call assert_true(groupcount > 0)
   let matchcount = len('File'->getcompletion('event'))
@@ -527,9 +519,7 @@
 endfunc
 
 func Test_cmdline_keymap_ctrl_hat()
-  if !has('keymap')
-    return
-  endif
+  CheckFeature keymap
 
   set keymap=esperanto
   call feedkeys(":\"Jxauxdo \<C-^>Jxauxdo \<C-^>Jxauxdo\<CR>", 'tx')
@@ -596,8 +586,7 @@
       call feedkeys(':e ~' . first_letter . "\<c-a>\<c-B>\"\<cr>", 'tx')
       call assert_match('^"e \~.*\<' . whoami . '\>', @:)
     endif
-  endif
-  if has('win32')
+  elseif has('win32')
     " Just in case: check that the system has an Administrator account.
     let names = system('net user')
     if names =~ 'Administrator'
@@ -606,14 +595,15 @@
       call feedkeys(':e ~A' . "\<c-a>\<c-B>\"\<cr>", 'tx')
       call assert_match('^"e \~.*Administrator', @:)
     endif
+  else
+    throw 'Skipped: does not work on this platform'
   endif
 endfunc
 
 func Test_cmdline_complete_bang()
-  if executable('whoami')
-    call feedkeys(":!whoam\<C-A>\<C-B>\"\<CR>", 'tx')
-    call assert_match('^".*\<whoami\>', @:)
-  endif
+  CheckExecutable whoami
+  call feedkeys(":!whoam\<C-A>\<C-B>\"\<CR>", 'tx')
+  call assert_match('^".*\<whoami\>', @:)
 endfunc
 
 func Test_cmdline_complete_languages()
@@ -1256,9 +1246,7 @@
 
 " Test for the :! command
 func Test_cmd_bang()
-  if !has('unix')
-    return
-  endif
+  CheckUnix
 
   let lines =<< trim [SCRIPT]
     " Test for no previous command