test: rollback transaction in tests relying on Spanner emulator

[chenba]

We need to explicitly rollback transactions in tests that rely on the Spanner emulator.

Closes STOR-388 / #1850

[pjenvey]

In the original issue I had an idea for making a wrapper similar to db_pool.transaction_http/http -- do you think that's feasible?

It would be more explicit than requiring the Drop and requiring the tests to call rollback themselves. One issue with the manual rollback is if any part of the test fails for whatever reason, that rollback won't be called.

It could be a noop on the backends that support test_transactions or it could replace that feature entirely.

[chenba]

In the original issue I had an idea for making a wrapper similar to db_pool.transaction_http/http -- do you think that's feasible?

I'll take a look.

It would be more explicit than requiring the Drop and requiring the tests to call rollback themselves. One issue with the manual rollback is if any part of the test fails for whatever reason, that rollback won't be called.

I misinterpreted your request for making things explicit. Drop works without the other changes. As it is in this PR, the Drop is conditional so that if the test failed to rollback then Drop handles it. But we could just as well remove the "explicit" rollback in the test and let Drop handle it every time.

[chenba]

Added with_transaction, similar to db_pool.transaction_http, that wraps a test in a transaction, and ensures the rollback. The test updates are mostly whitespace from the additional indentation. h/t @pjenvey

[pjenvey]

awesome, thanks for this

[pjenvey]

nit/not blocking this PR/more of an FYI: there's a Rust idiom where you can avoid the need for Some() here: Into<Option<_>>

[pjenvey]

Maybe call this test_transaction or with_test_transaction? Especially as it's along similar lines of the use_test_transactions setting which calls diesel's begin_test_transaction.

Which reminds me, diesel even has essentially its own version of this it just calls test_transaction FYI