You can use `maparg` to be a little more direct in your check.  This will also allow you to say `<leader>` rather than `\`. So a check (in vim) would look like:

``` vim
echo maparg('<leader>gj', 'n')
" => returns CtlrP app/assets/javascripts<cr>
```

and this ruby method could be:

``` ruby
def mapping_output(keys, mode='n')
  vim.command "echo maparg('#{keys}', '#{mode}')"
end
```