2 files changed, 31 insertions, 10 deletions
diff --git a/test/functional/eval/system_spec.lua b/test/functional/eval/system_spec.lua
index b8f1f87f30..6393477260 100644
--- a/test/functional/eval/system_spec.lua
+++ b/test/functional/eval/system_spec.lua
@@ -1,6 +1,7 @@
 local helpers = require('test.functional.helpers')(after_each)
-local eq, clear, eval, feed, nvim =
-  helpers.eq, helpers.clear, helpers.eval, helpers.feed, helpers.nvim
+local eq, clear, eval, execute, feed, nvim =
+  helpers.eq, helpers.clear, helpers.eval, helpers.execute, helpers.feed,
+  helpers.nvim
 
 local Screen = require('test.functional.ui.screen')
 
@@ -117,8 +118,12 @@ describe('system()', function()
       eq("echoed", eval('system("echo -n echoed")'))
     end)
     it('to backgrounded command does not crash', function()
-      -- This is indeterminate, just exercise the codepath.
-      eval('system("echo -n echoed &")')
+      -- This is indeterminate, just exercise the codepath. May get E5677.
+      execute('call system("echo -n echoed &")')
+      local v_errnum = string.match(eval("v:errmsg"), "^E%d*:")
+      if v_errnum then
+        eq("E5677:", v_errnum)
+      end
       eq(2, eval("1+1"))  -- Still alive?
     end)
   end)
@@ -128,8 +133,12 @@ describe('system()', function()
       eq("input", eval('system("cat -", "input")'))
     end)
     it('to backgrounded command does not crash', function()
-      -- This is indeterminate, just exercise the codepath.
-      eval('system("cat - &", "input")')
+      -- This is indeterminate, just exercise the codepath. May get E5677.
+      execute('call system("cat - &")')
+      local v_errnum = string.match(eval("v:errmsg"), "^E%d*:")
+      if v_errnum then
+        eq("E5677:", v_errnum)
+      end
       eq(2, eval("1+1"))  -- Still alive?
     end)
   end)
diff --git a/test/functional/helpers.lua b/test/functional/helpers.lua
index 325f41e506..3598ab5e6e 100644
--- a/test/functional/helpers.lua
+++ b/test/functional/helpers.lua
@@ -1,11 +1,13 @@
 require('coxpcall')
 local lfs = require('lfs')
-local ChildProcessStream = require('nvim.child_process_stream')
-local SocketStream = require('nvim.socket_stream')
-local TcpStream = require('nvim.tcp_stream')
-local Session = require('nvim.session')
 local global_helpers = require('test.helpers')
 
+-- nvim client: Found in .deps/usr/share/lua/<version>/nvim/ if "bundled".
+local Session = require('nvim.session')
+local TcpStream = require('nvim.tcp_stream')
+local SocketStream = require('nvim.socket_stream')
+local ChildProcessStream = require('nvim.child_process_stream')
+
 local check_logs = global_helpers.check_logs
 local neq = global_helpers.neq
 local eq = global_helpers.eq
@@ -134,10 +136,14 @@ local function stop()
   session:stop()
 end
 
+-- Executes an ex-command. VimL errors will manifest as client (lua) errors, and
+-- v:errmsg will be updated.
 local function nvim_command(cmd)
   request('nvim_command', cmd)
 end
 
+-- Evaluates a VimL expression.
+-- Fails on VimL error, but does not update v:errmsg.
 local function nvim_eval(expr)
   return request('nvim_eval', expr)
 end
@@ -158,10 +164,14 @@ local os_name = (function()
   end)
 end)()
 
+-- Executes a VimL function.
+-- Fails on VimL error, but does not update v:errmsg.
 local function nvim_call(name, ...)
   return request('nvim_call_function', name, {...})
 end
 
+-- Sends user input to Nvim.
+-- Does not fail on VimL error, but v:errmsg will be updated.
 local function nvim_feed(input)
   while #input > 0 do
     local written = request('nvim_input', input)
@@ -279,6 +289,8 @@ local function insert(...)
   nvim_feed('<ESC>')
 end
 
+-- Executes an ex-command by user input. Because nvim_input() is used, VimL
+-- errors will not manifest as client (lua) errors. Use command() for that.
 local function execute(...)
   for _, v in ipairs({...}) do
     if v:sub(1, 1) ~= '/' then