[hibernate-dev] Making tests nicer with lambdas

[Gunnar Morling]

Hey,

I've played around a bit with the idea of using Java 8 lambdas to make
tests easier to write and read. We have many tests which open a session and
TX, do some stuff, commit, open a new TX (and/or session), do some
assertions and so on:

    Session session = openSession();
  Transaction transaction = session.beginTransaction();

    // heavy testing action...
    transaction.commit();
  session.clear();

    transaction = session.beginTransaction();

    // load, assert...
  transaction.commit();
  session.clear();

The same could look like this using Java 8 lambdas:

    Foo foo = inTransactionWithResult( (session, tx) -> {
        // heavy testing action...
  } );

    inTransaction( (session, tx) -> {
        // load, assert...
  } );

Extracting the session/TX handling removes quite some clutter and focuses
more on the actual testing logic. It also avoids problems due to dangling
transactions e.g. in case of assertion failures as the TX handling is done
in a finally block in inTransaction().

At this point I've just done a quick POC and would be interested in
feedback whether you think that's worth pursuing or not. Note that
different language levels can be used for test and main code, so we could
make use of lambdas in tests while ensuring Java 6 compatibility for the
delivered artifacts.

--Gunnar