refactor(context): Phase2 上下文引擎升级 分层记忆+压缩+隔离 [v2026.07.19.4]

backend/python/tests/test_context_engine.py

@@ -0,0 +1,114 @@
+"""Phase 2 context-engine regression: _build_chat_history budget/layering/summary.
+
+Pure unit test with a fake DB session — no network, no real model. Guards the
+layered-memory + compression + isolation behaviour against regressions.
+"""
+from app.api.chat_context import _estimate_tokens, _build_chat_history
+
+
+class _Msg:
+    def __init__(self, role, content, cid="c1"):
+        self.role = role
+        self.content = content
+        self.conversation_id = cid
+
+
+class _Summary:
+    def __init__(self, text):
+        self.summary_text = text
+
+
+class _Query:
+    def __init__(self, rows):
+        self._rows = list(rows)
+
+    def filter(self, *a, **k):
+        return self
+
+    def order_by(self, *a, **k):
+        # test pre-sorts newest-first to match desc(created_at)
+        return self
+
+    def limit(self, n=None):
+        return self
+
+    def all(self):
+        return self._rows
+
+    def first(self):
+        return self._rows[0] if self._rows else None
+
+
+class _DB:
+    def __init__(self, messages, summary=None):
+        self._messages = messages
+        self._summary = summary
+
+    def query(self, model):
+        if getattr(model, "__name__", "") == "ConversationSummary":
+            return _Query([self._summary] if self._summary else [])
+        return _Query(self._messages)
+
+
+def _newest_first(msgs):
+    # _build_chat_history expects desc(created_at) -> newest first.
+    # Test authors write the list already newest-first, so return as-is.
+    return list(msgs)
+
+
+def test_estimate_tokens():
+    assert _estimate_tokens("") == 0
+    assert _estimate_tokens(None) == 0
+    assert _estimate_tokens("abcd") == 2  # 4//2
+    assert _estimate_tokens("a" * 5) == 2  # max(1, 5//2)=2
+    # just ensure positive monotonic
+    assert _estimate_tokens("x" * 100) == 50
+
+
+def test_history_excludes_latest_user():
+    # newest-first: [current user, prev assistant, older user]
+    msgs = _newest_first([
+        _Msg("user", "current question"),
+        _Msg("assistant", "previous answer"),
+        _Msg("user", "older question"),
+    ])
+    db = _DB(msgs)
+    out = _build_chat_history(db, "c1", max_tokens=10000, exclude_latest_user=True)
+    roles = [m["role"] for m in out]
+    # current user dropped; chronological order = [older user, previous assistant]
+    assert roles == ["user", "assistant"]
+    assert out[0]["content"] == "older question"
+
+
+def test_summary_injected_as_system_first():
+    msgs = _newest_first([
+        _Msg("user", "hi"),
+        _Msg("assistant", "hello"),
+    ])
+    db = _DB(msgs, summary=_Summary("用户想做图片生成"))
+    out = _build_chat_history(db, "c1", max_tokens=10000, exclude_latest_user=True)
+    assert out[0]["role"] == "system"
+    assert out[0]["content"].startswith("【对话历史摘要")
+    assert "用户想做图片生成" in out[0]["content"]
+    # after summary: chronological history (assistant then user 'hi' excluded? exclude_latest_user drops 'hi')
+    assert out[1]["role"] == "assistant"
+
+
+def test_budget_truncation():
+    # 5 assistant messages each ~200 tokens; budget small -> truncated
+    msgs = _newest_first([_Msg("assistant", "x" * 400) for _ in range(5)])
+    db = _DB(msgs)
+    out = _build_chat_history(db, "c1", max_tokens=500, exclude_latest_user=False)
+    # each msg ~200 tokens; budget 500 -> keep newest ~2
+    assert len(out) <= 3
+    total = sum(_estimate_tokens(m["content"]) for m in out)
+    assert total <= 500 + 200  # within budget (+1 msg slack)
+
+
+def test_no_summary_when_absent():
+    msgs = _newest_first([_Msg("user", "hi"), _Msg("assistant", "hello")])
+    db = _DB(msgs)
+    out = _build_chat_history(db, "c1", max_tokens=10000, exclude_latest_user=True)
+    # 'hi' excluded; only assistant remains, no system summary
+    assert all(m["role"] != "system" for m in out)
+    assert [m["role"] for m in out] == ["assistant"]