ai-agent-book 精选快照（<2MB 代码与文档，来自 github.com/bojieli/ai-agent-book）

chapter4/execution-tools/test_truncate_tail_lines_zero.py

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+"""tail_lines=0 must keep no tail lines (Python lines[-0:] quirk)."""
+from execution_tools import truncate_and_persist
+
+
+def test_tail_lines_zero_keeps_only_head():
+    text = "\n".join(f"line{i}" for i in range(100))
+    out, path = truncate_and_persist(
+        text, head_lines=3, tail_lines=0, max_lines=10, max_chars=50
+    )
+    assert path is not None
+    assert "line0" in out and "line1" in out and "line2" in out
+    assert "line99" not in out
+    assert "line50" not in out
+    assert out.count("line0") == 1
+
+
+def test_tail_lines_positive_still_keeps_tail():
+    text = "\n".join(f"line{i}" for i in range(100))
+    out, path = truncate_and_persist(
+        text, head_lines=2, tail_lines=2, max_lines=10, max_chars=50
+    )
+    assert path is not None
+    assert "line0" in out and "line1" in out
+    assert "line98" in out and "line99" in out
+    assert "line50" not in out
+
+
+def test_short_file_char_overflow_does_not_duplicate_lines():
+    text = ("x" * 4000 + "\n") * 3
+    out, path = truncate_and_persist(
+        text, head_lines=50, tail_lines=50, max_lines=200, max_chars=100
+    )
+    assert path is not None
+    # Three content lines plus the guide line — no head/tail duplication.
+    content_lines = [ln for ln in out.split("\n") if ln.startswith("x")]
+    assert len(content_lines) == 3