test: 'shadafile' default

ref 773bdd41ec

test/functional/helpers.lua

@@ -351,12 +351,13 @@ end
 
 -- Starts a new global Nvim session.
 -- Parameters are interpreted as startup args, OR a map with these keys:
---    args: Merged with the default `nvim_argv` set.
+--    args: Appended to the default `nvim_argv` set.
 --    env : Defines the environment of the new session.
+--    headless: Append --headless arg.
 --
 -- Example:
 --    clear('-e')
---    clear({args={'-e'}, env={TERM=term}})
+--    clear{args={'-e'}, env={TERM=term}}
 local function clear(...)
   local args = {unpack(nvim_argv)}
   local new_args