Before tmp-postgres existed I used pg_tmp for my testing purposes. pg_tmp is a great little utility which I still use when I want to do some quick throwaway postgres testing.
I just have to type:
$ psql $(pg_tmp)
and I get a client to play around with a ephemeral postgres.
However I found the lack of prompt resource clean up problematic when running automatic tests.
To ensure that the temporary postgres resources were cleaned up reliably tmp-postgres was born.
tmp-postgres started as a file in a package. I then copied it to another package and as I was about to copy it to a third package I realized it should live as a standalone project.