public async Task DefaultIfEmptyShouldReturnDefaultValueOnEmptySequence()
{
var sequence1 = await AsyncEnumerable.Empty<int>().DefaultIfEmpty().ToList();
CollectionAssert.AreEqual(new [] { 0 },sequence1.ToList());
var sequence2 = await AsyncEnumerable.Range(0, 2).DefaultIfEmpty().ToList();
CollectionAssert.AreEqual(new [] { 0,1},sequence2.ToList());
}
}