function! ToggleTestAutoGroup()
    let l:enable = exists('#TestAutoGroup#BufEnter')
    augroup TestAutoGroup
        autocmd!
    augroup END
    if !l:enable
        augroup TestAutoGroup
            autocmd BufEnter   * echom "BufEnter " . bufnr("%")
            autocmd BufLeave   * echom "BufLeave " . bufnr("%")
            autocmd TabEnter   * echom "TabEnter " . tabpagenr()
            autocmd TabLeave   * echom "TabLeave " . tabpagenr()
        augroup END
    endif
endfunction

nnoremap <F4> :call ToggleTestAutoGroup()<CR>