test: 单元测试与端到端冒烟

88 个测试覆盖配置继承、注册表、GPU 守卫、YOLO 格式解析、数据集、模型形状、
标签模式、聚类原语与 SimCLR 损失，以及 train.py / eval.py / 聚类脚本的入口接线。

含两条回归测试：
- PCA 白化放大噪声方向导致簇塌陷（默认 whiten=False 的依据）
- classes 写成 data.yaml 路径时 num_classes 必须是类别数而非路径字符串长度

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/test_visualizer.py

@@ -0,0 +1,63 @@
+"""SwanLab 可视化封装：可用时记录，不可用时必须静默降级、不影响训练。"""
+
+import builtins
+
+import pytest
+
+from engine.visualizer import SwanLabLogger
+
+
+def test_disabled_logger_is_noop(tmp_path):
+    logger = SwanLabLogger(enabled=False, work_dir=tmp_path)
+    assert logger.enabled is False
+    logger.log({"loss": 1.0}, step=1)
+    logger.finish()
+
+
+def test_mode_disabled_is_treated_as_off(tmp_path):
+    assert SwanLabLogger(work_dir=tmp_path, mode="disabled").enabled is False
+
+
+def test_invalid_mode_raises(tmp_path):
+    with pytest.raises(ValueError, match="swanlab mode"):
+        SwanLabLogger(work_dir=tmp_path, mode="cloud")
+
+
+def test_missing_swanlab_degrades_gracefully(tmp_path, monkeypatch):
+    real_import = builtins.__import__
+
+    def fake_import(name, *args, **kwargs):
+        if name == "swanlab":
+            raise ImportError("no swanlab")
+        return real_import(name, *args, **kwargs)
+
+    monkeypatch.setattr(builtins, "__import__", fake_import)
+    logger = SwanLabLogger(work_dir=tmp_path)
+    assert logger.enabled is False
+    logger.log({"loss": 1.0})  # 不应抛异常
+
+
+def test_offline_run_records_metrics(tmp_path):
+    pytest.importorskip("swanlab")
+    logger = SwanLabLogger(
+        work_dir=tmp_path, project="mte-tests", mode="offline", config={"lr": 0.1}
+    )
+    if not logger.enabled:  # 环境不允许起 run 时跳过，不让测试变脆
+        pytest.skip("swanlab 无法在当前环境初始化")
+    logger.log({"total": 1.0, "lr": 0.1}, step=1, prefix="train/")
+    logger.finish()
+    assert (tmp_path / "swanlog").exists()
+
+
+def test_log_failure_disables_instead_of_raising(tmp_path):
+    logger = SwanLabLogger(enabled=False, work_dir=tmp_path)
+    logger.enabled = True  # 伪造已启用但底层不可用的状态
+
+    class Broken:
+        @staticmethod
+        def log(*args, **kwargs):
+            raise RuntimeError("network down")
+
+    logger._swanlab = Broken()
+    logger.log({"loss": 1.0}, step=1)
+    assert logger.enabled is False