A testing-only transaction manager which replaces nested transactions with savepoints

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It is currently a bit challenging to write integration tests for (user) product code which explicitly manages transactions. Since database don't support nested transactions, users can't run the entire test in a transaction and roll it back (to avoid test interference, as can be done with tests which don't manage transactions). This causes the following difficulties:

• The database needs to be reverted to its initial state after every test runs, which can be tricky.
• Test parallelization must be disabled.

We could provide an IDbContextTransactionManager which "implements" nested transactions as savepoints. That is, if BeginTransaction is called and a transaction already exists, we could create a savepoint instead. This would allow the test to fully manage transactions, but without ever actually committing anything, working around the issues above.

Originally discussed in npgsql/npgsql#3982

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@AndriySvyryd this may not be useful in scenarios where multiple contexts are used (since the transaction needs to be shared). See:

efcore/test/EFCore.Specification.Tests/TestUtilities/TestHelpers.cs

Line 281 in dbc4314

public static void ExecuteWithStrategyInTransaction<TContext>(

[yori-s]

Is there a quick and dirty solution for code that (a) doesn't explicitly set transaction boundaries and (b) tests don't run in parallel?

I recently had a really nice experience with a rails/pg app where tests needed minimal scaffolding (thanks to factorybot), cleaned up after themselves, and ran in good time.