feat: 多专业小模型+路由模型系统 MVP（mock 全链路 + FastAPI 网关 + 论文调研）

tests/test_classifier.py

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+"""分类器单元测试。"""
+from router_system.classifier import RuleClassifier
+
+
+def test_code_classification():
+    clf = RuleClassifier()
+    r = clf.classify("用 Python 写一个快速排序函数")
+    assert r.domain == "code"
+    assert r.confidence > 0.7
+
+
+def test_math_classification():
+    clf = RuleClassifier()
+    r = clf.classify("求解方程 x^2 - 5x + 6 = 0")
+    assert r.domain == "math"
+    assert r.confidence > 0.7
+
+
+def test_legal_classification():
+    clf = RuleClassifier()
+    r = clf.classify("劳动合同到期不续签需要支付经济补偿吗")
+    assert r.domain == "legal"
+
+
+def test_medical_classification():
+    clf = RuleClassifier()
+    r = clf.classify("高血压患者日常饮食需要注意什么")
+    assert r.domain == "medical"
+
+
+def test_general_low_confidence():
+    clf = RuleClassifier()
+    r = clf.classify("今天天气怎么样")
+    # 未命中任何领域 -> 低置信度，触发 should_fallback
+    assert r.domain == "general"
+    assert clf.should_fallback(r, 0.6) is True
+
+
+def test_difficulty_estimation():
+    clf = RuleClassifier()
+    easy = clf.classify("1 + 1 = ?")
+    hard = clf.classify("证明费马大定理并推导其推论，给出详细步骤")
+    assert hard.difficulty in ("medium", "hard")
+    assert easy.difficulty == "easy"␍