The capture_items fixture unconditionally accesses json["attributes"] (line 353), but _span_batcher._to_transport_format only includes the attributes key when item._attributes is truthy (line 116-119 in _span_batcher.py). While in practice StreamedSpan.end() always sets segment attributes, this creates a fragile dependency on implementation details. If a span somehow ends up without attributes (e.g., through mocking or future code changes), the fixture will raise a KeyError.