diff --git a/tests/api/handlers/base/test_stream_processor.py b/tests/api/handlers/base/test_stream_processor.py
new file mode 100644
index 0000000..fa189fa
--- /dev/null
+++ b/tests/api/handlers/base/test_stream_processor.py
@@ -0,0 +1,32 @@
+from typing import Any, Dict, Optional
+
+from src.api.handlers.base.response_parser import ParsedChunk, ParsedResponse, ResponseParser, StreamStats
+from src.api.handlers.base.stream_context import StreamContext
+from src.api.handlers.base.stream_processor import StreamProcessor
+from src.utils.sse_parser import SSEEventParser
+
+
+class DummyParser(ResponseParser):
+    def parse_sse_line(self, line: str, stats: StreamStats) -> Optional[ParsedChunk]:
+        return None
+
+    def parse_response(self, response: Dict[str, Any], status_code: int) -> ParsedResponse:
+        return ParsedResponse(raw_response=response, status_code=status_code)
+
+    def extract_usage_from_response(self, response: Dict[str, Any]) -> Dict[str, int]:
+        return {}
+
+    def extract_text_content(self, response: Dict[str, Any]) -> str:
+        return ""
+
+
+def test_process_line_strips_newlines_and_finalizes_event() -> None:
+    ctx = StreamContext(model="test-model", api_format="OPENAI")
+    processor = StreamProcessor(request_id="test-request", default_parser=DummyParser())
+    sse_parser = SSEEventParser()
+
+    processor._process_line(ctx, sse_parser, 'data: {"type":"response.completed"}\n')
+    processor._process_line(ctx, sse_parser, "\n")
+
+    assert ctx.has_completion is True
+