"One of the most essential practices for maintaining the long-term quality of computer code is to write automated tests that ensure the program continues to act as expected, even when other people (including your future self) muck with it."
That's such a great condensation of why automated tests are worthwhile.
"To write your own testing framework based on continuation trees, all you need is a stack of databases (or rather, a database that supports rolling back to an arbitrary revision)."
PostgreSQL and SQLite and MySQL all support SAVEPOINT these days, which is a way to have a transaction nested inside a transaction. I could imagine building a testing system on top of this which could support the tree pattern described by Evan here (as long as your tests don't themselves need to test transaction-related behavior).
An approach we've done is to use Postgres' "create database foo2 template foo1" syntax to essentially snapshot the db under test at various points and use those to rollback as needed.
I feel uneasy about using transactions like that. Eventually somebody will be puzzled enough to enable statement logging, which will not contain the data they need. Then they'll set a breakpoint in the test and get a shell on the db to see what's actually there, and they'll find it empty.
And by eventually somebody, I mean two days ago me.
I'd much rather just have a utility that copies the database actually and hands my test the one it's allowed to mess with.
One trick I've experimented with is setting things up so that if an assertion fails a copy of the full current state of the database is automatically captured and written out to a file on disk.
That's such a great condensation of why automated tests are worthwhile.
"To write your own testing framework based on continuation trees, all you need is a stack of databases (or rather, a database that supports rolling back to an arbitrary revision)."
PostgreSQL and SQLite and MySQL all support SAVEPOINT these days, which is a way to have a transaction nested inside a transaction. I could imagine building a testing system on top of this which could support the tree pattern described by Evan here (as long as your tests don't themselves need to test transaction-related behavior).
Since ChatGPT Code Interpreter works with o3-mini now I had that knock up a very quick proof of concept using Python and SQLite SAVEPOINT, which appears to work: https://chatgpt.com/share/67d36883-4294-8006-b464-4d6f937d99...