First workable version.

Able to define steps in the following way:
(When "I put :arg-1 into the buffer :arg-2"
      (lambda (text buffer-name)
        (...)))

And then it is able to use such step:

When I put "lorem ipsum" into the buffer 'test

Or in the code:

(When "I put :arg-1 into the buffer :arg-2" "text" "test")