feat(logging): include test-id in log messages

Problem:
1. Log messages (especially in CI) are hard to correlate with tests.
2. Since b353a5c05f02 #11886, dumplog() prints the logs next to test
   failures. This is noisy and gets in the way of the test results.

Solution:
1. Associate an incrementing id with each test and include it in log
   messages.
    - FUTURE: add v:name so Nvim instances can be formally "named"?
2. Mention "child" in log messages if the current Nvim is a child (based
   on the presence of $NVIM).

BEFORE:

    DBG … 12345      UI: event
    DBG … 12345      log_server_msg:722: RPC ->ch 1: …
    DBG … 12345      UI: flush
    DBG … 12345      inbuf_poll:444: blocking... events_enabled=1 events_pending=0
    DBG … 23454      UI: stop
    INF … 23454      os_exit:594: Nvim exit: 0

AFTER:

    DBG … T57        UI: event
    DBG … T57        log_server_msg:722: RPC ->ch 1: …
    DBG … T57        UI: flush
    DBG … T57        inbuf_poll:444: blocking... events_enabled=1 events_pending=0
    DBG … T57/child  UI: stop
    INF … T57/child  os_exit:594: Nvim exit: 0

1 files changed, 5 insertions, 20 deletions

diff --git a/test/helpers.lua b/test/helpers.lua
index 7d2f8f760a..f37af9d08d 100644
--- a/test/helpers.lua
+++ b/test/helpers.lua
@@ -40,10 +40,6 @@ function module.popen_r(...)
   return io.popen(module.argss_to_cmd(...), 'r')
 end
 
-function module.popen_w(...)
-  return io.popen(module.argss_to_cmd(...), 'w')
-end
-
 -- sleeps the test runner (_not_ the nvim instance)
 function module.sleep(ms)
   luv.sleep(ms)
@@ -104,16 +100,16 @@ end
 ---
 ---@param pat string      Lua pattern to search for in the log file
 ---@param logfile string  Full path to log file (default=$NVIM_LOG_FILE)
-function module.assert_log(pat, logfile)
+---@param nrlines number  Search up to this many log lines
+function module.assert_log(pat, logfile, nrlines)
   logfile = logfile or os.getenv('NVIM_LOG_FILE') or '.nvimlog'
-  local nrlines = 10
+  nrlines = nrlines or 10
   local lines = module.read_file_list(logfile, -nrlines) or {}
   for _,line in ipairs(lines) do
     if line:match(pat) then return end
   end
-  local logtail = module.read_nvim_log(logfile)
   error(string.format('Pattern %q not found in log (last %d lines): %s:\n%s',
-    pat, nrlines, logfile, logtail))
+    pat, nrlines, logfile, '    '..table.concat(lines, '\n    ')))
 end
 
 -- Invokes `fn` and returns the error string (with truncated paths), or raises
@@ -271,7 +267,7 @@ module.uname = (function()
       return platform
     end
 
-    if os.getenv("SYSTEM_NAME") then  -- From CMAKE_SYSTEM_NAME.
+    if os.getenv("SYSTEM_NAME") then  -- From CMAKE_HOST_SYSTEM_NAME.
       platform = string.lower(os.getenv("SYSTEM_NAME"))
       return platform
     end
@@ -409,17 +405,6 @@ function module.check_cores(app, force)
   end
 end
 
-function module.which(exe)
-  local pipe = module.popen_r('which', exe)
-  local ret = pipe:read('*a')
-  pipe:close()
-  if ret == '' then
-    return nil
-  else
-    return ret:sub(1, -2)
-  end
-end
-
 function module.repeated_read_cmd(...)
   for _ = 1, 10 do
     local stream = module.popen_r(...)