Given vim:
  command! -nargs=+    TestIt call s:func(<f-args>)
  execute "command! -nargs=0    TestFlip let s:var = 'hello'"
  execute 'let s:var = "bar"'
  echomsg s:var
  function! s:nested(a, b)
    TestIt
    TestFlip
  endfunc

Execute (:call lookup#lookup() to find definition of commands):
  " on TestIt
  normal! 6G
  AssertEqual [6, 3], [line('.'), col('.')]
  call lookup#lookup()
  AssertEqual [1, 22], [line('.'), col('.')]

  " on TestFlip
  normal! 7G
  call lookup#lookup()
  AssertEqual [2, 31], [line('.'), col('.')]