Write comprehensive unit tests for this function. Cover all edge cases, including boundary conditions, error cases, and typical usage. ```python def merge_sorted_streams(*streams, max_items=None): """ Merge multiple sorted iterables into a single sorted output. Args: *streams: Variable number of sorted iterables max_items: Optional limit on total items to yield Yields: Items from all streams in sorted order Raises: ValueError: If any stream is not sorted """ import heapq heap = [] iterators = [iter(s) for s in streams] # Initialize heap with first item from each stream for i, it in enumerate(iterators): try: item = next(it) heapq.heappush(heap, (item, i)) except StopIteration: pass count = 0 prev = None while heap and (max_items is None or count < max_items): item, stream_idx = heapq.heappop(heap) # Validate sorting if prev is not None and item < prev: raise ValueError(f"Stream {stream_idx} is not sorted") yield item prev = item count += 1 # Get next item from same stream try: next_item = next(iterators[stream_idx]) heapq.heappush(heap, (next_item, stream_idx)) except StopIteration: pass ``` Use pytest. Include parametrized tests where appropriate.