cannot run vimux with vim variable

[Syn3iotiC]

I want to map this key to vimux
nmap <leader>q :call VimuxRunCommand("api/rake spec SPEC=spec/requests/%:t")<cr>

%t in vim mean current filename.

But it doesn't work becuase vimux doesn't know how to interpret %:t as hello_spec.rb.

EDIT: Make it work by using this instead
nmap <leader>q :call VimuxRunCommand("api/rake spec SPEC=spec/requests/" . expand("%:t"))<cr>
Any suggestions?