def test_commit_filter():
ref_collection = Collection([(1,2),(2,3),(3,4)])
# test impossible filter
col1 = ref_collection.factory(ref_collection)
t1 = Transaction(col1)
t1._commit_filter([lambda x: False])
assert col1.data == []
# something more reasonable
col2 = ref_collection.factory(ref_collection)
t2 = Transaction(col2)
t2._commit_filter([lambda x: x[0] > 2])
assert len(col2) == 1
assert set(col2) < set(ref_collection)
