patch 8.2.1803: a few failures are not tested

Problem:    A few failures are not tested.
Solution:   Test a few failures. (Dominique Pellé, closes #7075)
diff --git a/src/testdir/test_arglist.vim b/src/testdir/test_arglist.vim
index 615d816..f45a0d4 100644
--- a/src/testdir/test_arglist.vim
+++ b/src/testdir/test_arglist.vim
@@ -426,6 +426,7 @@
   call assert_fails('argdelete', 'E610:')
   call assert_fails('1,100argdelete', 'E16:')
   call assert_fails('argdel /\)/', 'E55:')
+  call assert_fails('1argdel 1', 'E474:')
 
   call Reset_arglist()
   args a b c d
@@ -478,13 +479,16 @@
   new
   " redefine arglist; go to Xxx1
   next! Xxx1 Xxx2 Xxx3
-  " open window for all args
+  " open window for all args; Reading Xxx2 will change the arglist and the
+  " third window will get Xxx1:
+  "   win 1: Xxx1
+  "   win 2: Xxx2
+  "   win 3: Xxx1
   all
   call assert_equal('test file Xxx1', getline(1))
   wincmd w
   wincmd w
   call assert_equal('test file Xxx1', getline(1))
-  " should now be in Xxx2
   rewind
   call assert_equal('test file Xxx2', getline(1))
 
diff --git a/src/testdir/test_cmdline.vim b/src/testdir/test_cmdline.vim
index 026625e..9557828 100644
--- a/src/testdir/test_cmdline.vim
+++ b/src/testdir/test_cmdline.vim
@@ -756,6 +756,10 @@
   call feedkeys(":doautocmd User MyCmd a.c\<C-A>\<C-B>\"\<CR>", 'xt')
   call assert_equal("\"doautocmd User MyCmd a.c\<C-A>", @:)
 
+  " completion of autocmd group after comma
+  call feedkeys(":doautocmd BufNew,BufEn\<C-A>\<C-B>\"\<CR>", 'xt')
+  call assert_equal("\"doautocmd BufNew,BufEnter", @:)
+
   " completion for the :augroup command
   augroup XTest
   augroup END
diff --git a/src/testdir/test_json.vim b/src/testdir/test_json.vim
index 93597cb..f881ede 100644
--- a/src/testdir/test_json.vim
+++ b/src/testdir/test_json.vim
@@ -196,6 +196,7 @@
   call assert_fails('call json_decode("{[]:42}")', "E491:")
 
   call assert_fails('call json_decode("-")', "E491:")
+  call assert_fails('call json_decode("-1x")', "E491:")
   call assert_fails('call json_decode("infinit")', "E491:")
 
   call assert_fails('call json_decode("\"\\u111Z\"")', 'E491:')
diff --git a/src/testdir/test_listdict.vim b/src/testdir/test_listdict.vim
index 63fa04e..54486ff 100644
--- a/src/testdir/test_listdict.vim
+++ b/src/testdir/test_listdict.vim
@@ -726,6 +726,8 @@
   call assert_fails("call reduce({}, { acc, val -> acc + val }, 1)", 'E897:')
   call assert_fails("call reduce(0, { acc, val -> acc + val }, 1)", 'E897:')
   call assert_fails("call reduce('', { acc, val -> acc + val }, 1)", 'E897:')
+  call assert_fails("call reduce([1, 2], 'Xdoes_not_exist')", 'E117:')
+  call assert_fails("echo reduce(0z01, { acc, val -> 2 * acc + val }, '')", 'E39:')
 
   let g:lut = [1, 2, 3, 4]
   func EvilRemove()
diff --git a/src/version.c b/src/version.c
index 244c26d..e4bc870 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1803,
+/**/
     1802,
 /**/
     1801,