Most rspec test suites follow the convention of an inclusion filter for :focus tagged specs. I like to use guard-rspec to watch filesystem changes and run spec files. This plugin provides functions for easily adding and removing a :focus tag from the nearest spec, and writing the file, to trigger guard.
Add the plugin with you favorite plugin manager. Or do it manually. It's up to you, I won't judge.
Add two mappings - one for adding the :focus tag, and one for removing it. Below are mine - I use ff for adding focus, and FF for removing it.
nnoremap ff :call rspecfocus#AddFocusToPreviousRspecBlock()<CR>
nnoremap FF :call rspecfocus#RemoveAllFocus()<CR>
Use your mapping anywhere inside a spec file to add a :focus to the nearest spec block. If you're inside an it expectation, that will be focused. If you're inside a context or describe block, that will be focused.
It always looks backwards, to ensure the spec under your cursor is included in the focus.