Indeed, that's partly what my own testing framework (that I wrote and use on my own private projects) takes advantage of, except in interactive use.

The Common Lisp REPL automatically binds the last expression evaluated to the variable "+". It also automatically binds the value returned from the evaluation of the last expression to the variable "*".

I write code and develop interactively at the REPL with the package under development loaded/running. When the value I expect gets returned from the function or form I'm developing at the REPL, i just evaluate the "test" function (or a variant thereof if extra specificity or features are wanted such as names, doc-strings or tags, etc.), and the forms and expected values are packaged into a test and added to the projects' test repository.

Pretty much all the benefits of TDD, without writing tests up-front or wanting to do red/green (i did allow for the option, but i practically never do in practice), because they're an almost costless artifact of just developing now...