Impl Clone on DatabaseConnection

[robot-head]

I saw in #152 that DatabaseConnection was not marked Clone if mocks are enabled, but I see now that the Mock connection variant is behind an Arc.

Is there any reason not to make DatbaseConnection Clone? We've stuffed it into an Arc in our application code, but my code reviewers are questioning why the Arc is necessary.

[tyt2y3]

Yes he is right. Do not stuff an Arc in your app code.

Add a feature in your Cargo, and only enable Mock while in testing.

The reason behind that is Mock has a mock output buffer and a transaction log, where it will be hard to reason it's behaviour when being cloned and used across multiple threads.

[robot-head]

Thanks!

I might send ya a PR on the testing docs to help others that come across this

[PoOnesNerfect]

It seems like DatabaseConnection::MockDatabaseConnection has inner mock connection struct in an Arc, making it cloneable.
It seems strange that all variants of this DatabaseConnection derives Clone including Arc<MockDatabaseConnection>, but the wrapper enum itself does not implement Clone when mock feature is enabled.