Add check to ensure that IUserCollectionType.Instantiate returns uninitialized collection

[Sebazzz]

The documentation on IUserCollection.Instantiate already says that the collection needs to be uninitialized:

nhibernate-core/src/NHibernate/UserTypes/IUserCollectionType.cs

Lines 10 to 13 in dc71c7d

	/// <summary>
	/// Instantiate an uninitialized instance of the collection wrapper
	/// </summary>
	IPersistentCollection Instantiate(ISessionImplementor session, ICollectionPersister persister);

It would be nice to have a programmatic check that this assumption shall be true to prevent possible invalid or error-prone behaviour downstream.

[no149]

Interestingly , I ran into this issue a short time ago and I in my case it was because a generic IList could not be cast to a non-generic IList. The reference code lies In PersistentGenericList.cs: 42. That is from the source code for Build 3.3.4.GA.
One straightforward solution is to inherit your custom collection from a non-generic appropriate collection interface. Another(as we chose) is to map your collection as a private field and create a wrapper property around it to expose it.

[Sebazzz]

After some debugging I found out that this line, in the test, is the cause:

return new PersistentGenericSet<T>(session , new HashSet<T>(EqualityComparer<T>.Default));

Because the persistent collection is already given a wrapped collection, the persistent collection considers itself as initialized. Later on it is asked to check if it dirty, where it nullrefs because it hasn't got a snapshot (because it is considered initialized).

This is confusing API behavior, and probably a check needs to written that IUserCollectionType.Instantiate(ISessionImplementor, ICollectionPersister) doesn't return an initialized collection?

[Sebazzz]

Added the proposed check to the pull request and amended the test for this check.

[hazzik]

Took even longer to return here.

Can you please enable Allow edits from maintainers option on this PR?

The documentation on IUserCollection.Instantiate already says that the collection needs to be uninitialized:

nhibernate-core/src/NHibernate/UserTypes/IUserCollectionType.cs

Lines 10 to 13 in dc71c7d

	/// <summary>
	/// Instantiate an uninitialized instance of the collection wrapper
	/// </summary>
	IPersistentCollection Instantiate(ISessionImplementor session, ICollectionPersister persister);

[hazzik]

The code need to be aligned with the NHibernate's conventions.

I have a cleanup fix in place, I'll push it when option mentioned earlier be enabled.

[hazzik]

Rebased and code cleaned up

[fredericDelaporte]

Lacking TestFixture attribute, causing it to not generate an async counterpart.

[hazzik]

True

[hazzik]

It does not generate async code because action delegate is declared outside of Assert.That(...)

[fredericDelaporte]

Ok, but it still should have the attribute for consistency with other tests.

[hazzik]

I've added the attribute