[TestFixture]
public class AbstractIdInBaseClassTests
{
    private abstract class BaseClass
    {
        public abstract int Id { get; set; }
    }

    private class Impl : BaseClass
    {
        public override int Id { get; set; }
    }

    [Test]
    public void TestSerialization()
    {
        var impl = new Impl { Id = 1 };

        var doc = impl.ToBsonDocument();

        var expected = new BsonDocument("_id", 1);
        Assert.AreEqual(expected, doc);
    }
}