vim-patch:8.2.1043: %a item in 'statusline' not tested

Problem:    %a item in 'statusline' not tested.
Solution:   Add a test. (Dominique Pellé, closes vim/vim#6318)
4014e2ceb0

Do not run test_statusline.vim in test_alot.vim
because test_statusline.vim runs separately in Vim since patch v8.2.0164.

src/nvim/testdir/test_alot.vim

@@ -37,7 +37,6 @@ source test_recover.vim
 source test_scroll_opt.vim
 source test_sort.vim
 source test_sha256.vim
-source test_statusline.vim
 source test_suspend.vim
 source test_syn_attr.vim
 source test_tabline.vim

src/nvim/testdir/test_statusline.vim

@@ -1,12 +1,12 @@
 " Test 'statusline'
 "
 " Not tested yet:
-"   %a
 "   %N
 "   %T
 "   %X
 
 source view_util.vim
+source check.vim
 source term_util.vim
 
 func s:get_statusline()
@@ -61,7 +61,19 @@ func Test_statusline_will_be_disabled_with_error()
 endfunc
 
 func Test_statusline()
-  new Xstatusline
+  CheckFeature quickfix
+
+  " %a: Argument list ({current} of {max})
+  set statusline=%a
+  call assert_match('^\s*$', s:get_statusline())
+  arglocal a1 a2
+  rewind
+  call assert_match('^ (1 of 2)\s*$', s:get_statusline())
+  next
+  call assert_match('^ (2 of 2)\s*$', s:get_statusline())
+  e Xstatusline
+  call assert_match('^ ((2) of 2)\s*$', s:get_statusline())
+
   only
   set laststatus=2
   set splitbelow