diff --git a/src/testdir/test_excmd.vim b/src/testdir/test_excmd.vim
index f830be8..2e137f0 100644
--- a/src/testdir/test_excmd.vim
+++ b/src/testdir/test_excmd.vim
@@ -591,4 +591,10 @@
   sandbox call Sandbox_tests()
 endfunc
 
+func Test_command_not_implemented_E319()
+  if !has('mzscheme')
+    call assert_fails('mzscheme', 'E319:')
+  endif
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab
diff --git a/src/testdir/test_functions.vim b/src/testdir/test_functions.vim
index 1cce8a0..936a2d0 100644
--- a/src/testdir/test_functions.vim
+++ b/src/testdir/test_functions.vim
@@ -1148,7 +1148,9 @@
   call assert_equal(2, charidx(a, 4))
   call assert_equal(3, charidx(a, 7))
   call assert_equal(-1, charidx(a, 8))
+  call assert_equal(-1, charidx(a, -1))
   call assert_equal(-1, charidx('', 0))
+  call assert_equal(-1, charidx(test_null_string(), 0))
 
   " count composing characters
   call assert_equal(0, charidx(a, 0, 1))
diff --git a/src/testdir/test_options.vim b/src/testdir/test_options.vim
index 54042d4..d789a46 100644
--- a/src/testdir/test_options.vim
+++ b/src/testdir/test_options.vim
@@ -1093,4 +1093,32 @@
   call delete('Xscroll')
 endfunc
 
+" Check that VIM_POSIX env variable influences default value of 'cpo' and 'shm'
+func Test_VIM_POSIX()
+  let saved_VIM_POSIX = getenv("VIM_POSIX")
+
+  call setenv('VIM_POSIX', "1")
+  let after =<< trim [CODE]
+    call writefile([&cpo, &shm], 'X_VIM_POSIX')
+    qall
+  [CODE]
+  if RunVim([], after, '')
+    call assert_equal(['aAbBcCdDeEfFgHiIjJkKlLmMnoOpPqrRsStuvwWxXyZ$!%*-+<>#{|&/\.;',
+          \            'AS'], readfile('X_VIM_POSIX'))
+  endif
+
+  call setenv('VIM_POSIX', v:null)
+  let after =<< trim [CODE]
+    call writefile([&cpo, &shm], 'X_VIM_POSIX')
+    qall
+  [CODE]
+  if RunVim([], after, '')
+    call assert_equal(['aAbBcCdDeEfFgHiIjJkKlLmMnoOpPqrRsStuvwWxXyZ$!%*-+<>;',
+          \            'S'], readfile('X_VIM_POSIX'))
+  endif
+
+  call delete('X_VIM_POSIX')
+  call setenv('VIM_POSIX', saved_VIM_POSIX)
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab
diff --git a/src/testdir/test_startup.vim b/src/testdir/test_startup.vim
index 2d5fdcb..6e81470 100644
--- a/src/testdir/test_startup.vim
+++ b/src/testdir/test_startup.vim
@@ -622,6 +622,12 @@
   endfor
 
   if has('gui_gtk')
+    let out = split(system(GetVimCommand() .. ' --socketid'), "\n")
+    call assert_equal(1, v:shell_error)
+    call assert_match('^VIM - Vi IMproved .* (.*)$',          out[0])
+    call assert_equal('Argument missing after: "--socketid"', out[1])
+    call assert_equal('More info with: "vim -h"',             out[2])
+
     for opt in ['--socketid x', '--socketid 0xg']
       let out = split(system(GetVimCommand() .. ' ' .. opt), "\n")
       call assert_equal(1, v:shell_error)
@@ -629,6 +635,7 @@
       call assert_equal('Invalid argument for: "--socketid"', out[1])
       call assert_equal('More info with: "vim -h"',           out[2])
     endfor
+
   endif
 endfunc
 
diff --git a/src/testdir/test_syntax.vim b/src/testdir/test_syntax.vim
index bc268a1..0a0d667 100644
--- a/src/testdir/test_syntax.vim
+++ b/src/testdir/test_syntax.vim
@@ -111,6 +111,9 @@
   let a = execute('syntime report')
   call assert_equal("\nNo Syntax items defined for this buffer", a)
 
+  let a = execute('syntime clear')
+  call assert_equal("\nNo Syntax items defined for this buffer", a)
+
   view ../memfile_test.c
   setfiletype cpp
   redraw
diff --git a/src/testdir/test_vim9_cmd.vim b/src/testdir/test_vim9_cmd.vim
index 1e1a498..080fe20 100644
--- a/src/testdir/test_vim9_cmd.vim
+++ b/src/testdir/test_vim9_cmd.vim
@@ -13,6 +13,7 @@
     vim9cm assert_equal('yes', y)
   END
   CheckScriptSuccess(lines)
+  assert_fails('vim9cmd', 'E1164:')
 enddef
 
 def Test_edit_wildcards()
diff --git a/src/version.c b/src/version.c
index 5ef8d7c..d9c6540 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2837,
+/**/
     2836,
 /**/
     2835,