run your tests in a separate tmux pane!

.vimrc

" when triggering this command, vim will grab your path and line location and pass it along
map <Leader>el :call RemoteSendCommand(TestLineCommand(expand("%:p"), line(".")))<CR>

" because I'm mostly writing Elixir and making heavy use of the REPL while writing my tests,
" I made a specifc command to user with Mix, the Elixir task utility
" But I'm sure you could get this to work with vim-test or something like that
function! TestLineCommand(path, line_number)
  let cmd = join(["mix test --only", " line:", a:line_number, " ", a:path], "")
  return cmd
endfunction

" Here, -t 6 specifies the pane you're sending the keys to
function! RemoteSendCommand(cmd)
  execute "! tmux send-keys -t 6 \"" . a:cmd . "\" C-m"
endfunction