Testing of MVCC

I want to write some regression tests that confirm the behavior of
multiple connections simultaneously going at the same tables/rows. Is
there something like this already, e.g. in src/test/regress? In
particular I want confirm the robustness of some PL/pgSQL functions in a
multi-user environment. I could probably just bang away from multiple
interactive psql sessions, but I like to script the whole thing, and I'd
like it all to fit neatly into the current "make check" regression
tests.