public void Flatten_WithEmptyEnumerable_ExpectsSameEnumerable() => Utilities.AssertManySequencesEqual( ENMRBL_EMPTY.Flatten(), ENMRBL_EMPTY);
public void Flatten_WithEmptyEnumerableAndNullProvider_Throws() => Throws <ArgumentNullException>( () => ENMRBL_EMPTY.Flatten(null).ToList());