test: 테스트 커버리지 77% → 80% 달성 (issue #204)

신규/추가 테스트:
- tests/test_logging_config.py: JSONFormatter, setup_logging 전체 커버 (14줄)
- tests/test_strategies_base.py: BaseStrategy 추상 클래스 커버 (6줄)
- tests/test_backup.py: BackupExporter 미커버 경로(빈 CSV, compress=True CSV,
  포맷 실패 로깅, 기본 formats) + CloudStorage boto3 모킹 테스트 20개 (113줄)
- tests/test_context.py: ContextSummarizer 전체 커버 22개 테스트 (50줄)

총 815개 테스트 통과, TOTAL 커버리지 80% (1046줄 미커버 / 5225줄 전체)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_logging_config.py

@@ -0,0 +1,117 @@
+"""Tests for JSON structured logging configuration."""
+
+from __future__ import annotations
+
+import json
+import logging
+import sys
+
+from src.logging_config import JSONFormatter, setup_logging
+
+
+class TestJSONFormatter:
+    """Test JSONFormatter output."""
+
+    def test_basic_log_record(self) -> None:
+        """JSONFormatter must emit valid JSON with required fields."""
+        formatter = JSONFormatter()
+        record = logging.LogRecord(
+            name="test.logger",
+            level=logging.INFO,
+            pathname="",
+            lineno=0,
+            msg="Hello %s",
+            args=("world",),
+            exc_info=None,
+        )
+        output = formatter.format(record)
+        data = json.loads(output)
+        assert data["level"] == "INFO"
+        assert data["logger"] == "test.logger"
+        assert data["message"] == "Hello world"
+        assert "timestamp" in data
+
+    def test_includes_exception_info(self) -> None:
+        """JSONFormatter must include exception info when present."""
+        formatter = JSONFormatter()
+        try:
+            raise ValueError("test error")
+        except ValueError:
+            exc_info = sys.exc_info()
+        record = logging.LogRecord(
+            name="test",
+            level=logging.ERROR,
+            pathname="",
+            lineno=0,
+            msg="oops",
+            args=(),
+            exc_info=exc_info,
+        )
+        output = formatter.format(record)
+        data = json.loads(output)
+        assert "exception" in data
+        assert "ValueError" in data["exception"]
+
+    def test_extra_trading_fields_included(self) -> None:
+        """Extra trading fields attached to the record must appear in JSON."""
+        formatter = JSONFormatter()
+        record = logging.LogRecord(
+            name="test",
+            level=logging.INFO,
+            pathname="",
+            lineno=0,
+            msg="trade",
+            args=(),
+            exc_info=None,
+        )
+        record.stock_code = "005930"  # type: ignore[attr-defined]
+        record.action = "BUY"  # type: ignore[attr-defined]
+        record.confidence = 85  # type: ignore[attr-defined]
+        record.pnl_pct = -1.5  # type: ignore[attr-defined]
+        record.order_amount = 1_000_000  # type: ignore[attr-defined]
+        output = formatter.format(record)
+        data = json.loads(output)
+        assert data["stock_code"] == "005930"
+        assert data["action"] == "BUY"
+        assert data["confidence"] == 85
+        assert data["pnl_pct"] == -1.5
+        assert data["order_amount"] == 1_000_000
+
+    def test_none_extra_fields_excluded(self) -> None:
+        """Extra fields that are None must not appear in JSON output."""
+        formatter = JSONFormatter()
+        record = logging.LogRecord(
+            name="test",
+            level=logging.INFO,
+            pathname="",
+            lineno=0,
+            msg="no extras",
+            args=(),
+            exc_info=None,
+        )
+        output = formatter.format(record)
+        data = json.loads(output)
+        assert "stock_code" not in data
+        assert "action" not in data
+        assert "confidence" not in data
+
+
+class TestSetupLogging:
+    """Test setup_logging function."""
+
+    def test_configures_root_logger(self) -> None:
+        """setup_logging must attach a JSON handler to the root logger."""
+        setup_logging(level=logging.DEBUG)
+        root = logging.getLogger()
+        json_handlers = [
+            h for h in root.handlers if isinstance(h.formatter, JSONFormatter)
+        ]
+        assert len(json_handlers) == 1
+        assert root.level == logging.DEBUG
+
+    def test_avoids_duplicate_handlers(self) -> None:
+        """Calling setup_logging twice must not add duplicate handlers."""
+        setup_logging()
+        setup_logging()
+        root = logging.getLogger()
+        assert len(root.handlers) == 1