Currently, the only thing that tests aggregation via the new API is CollectionAcceptance test. We should:

• Work out which tests, if any, that use the old API need porting to use the new API
• Find holes in the coverage and add tests.

In addition, there was an Ignored test in JavaClientOldTest:

public void testAggregateOnSecondary()

As it was ignored, this was not being run. But it's not clear why it was ignored or what it was trying to test. If this is an important test, we need to implement it using the new API.