feat: CLI coding agent bakeoff — 26b reproducibly silent-stops at write_file

Ran minimal agent loop (Ollama /api/chat + read_file/write_file/run_bash) on steel141 3090 Ti against 3 models on a broken-median-function task: - gemma4:31b-it-q4_K_M: PASS (8 iters, 1 write, 44s) — textbook trace - qwen3-coder:30b: PASS (15 iters, 1 write, 22s) — correct but chatty - gemma4:26b: FAIL (6 iters, 0 writes) — silently stops with eval=4 after reading source. Reproduced on second run. One-shot probe confirms 26b CAN produce the correct fix — failure is specifically at the write_file tool-call argument boundary. Updates GOTCHAS with a new HIGH-severity entry, SYNTHESIS model-selection table, CORPUS_cli_coding_agent.md empirical-follow-up pointer, and adds docs/reference/bakeoff-2026-04-18.md with the full writeup.
2026-04-18 13:27:50 -04:00
parent 4b9c537dda
commit a945207aab
15 changed files with 1172 additions and 1 deletions
@@ -0,0 +1,301 @@
+"""CLI coding agent bakeoff harness.
+
+Minimal agent loop: Ollama /api/chat with tools [read_file, write_file, run_bash].
+Non-streaming, think=false. Workdir sandboxed; path traversal blocked; bash
+timeout 30s; iteration cap 15.
+
+Invocation:
+    python3 harness.py <model-tag> <workdir> <log-path>
+
+Example:
+    python3 harness.py gemma4:26b runs/gemma4-26b/work runs/gemma4-26b/log.json
+"""
+
+from __future__ import annotations
+
+import json
+import os
+import shutil
+import subprocess
+import sys
+import time
+from pathlib import Path
+from urllib import request as urlreq
+
+OLLAMA_HOST = os.environ.get("OLLAMA_HOST", "http://127.0.0.1:11434")
+MAX_ITERATIONS = 15
+BASH_TIMEOUT_S = 30
+REQUEST_TIMEOUT_S = 540  # 9 min — keep inside the 10-min Bash ceiling
+
+SYSTEM_PROMPT = """You are a terminal coding agent.
+
+## What you do
+- Read source and test files to understand the code
+- Make targeted edits to fix bugs so the tests pass
+- Run pytest to verify your fix
+- Stop once all tests pass and reply with a one-sentence summary
+
+## What you do NOT do
+- Never modify files under tests/
+- Never disable, skip, or delete tests
+- Never write outside the working directory
+- Never call tools after all tests pass — just reply with the summary and stop
+
+## Available tools
+- read_file(path): read a file relative to the working directory
+- write_file(path, content): overwrite a file relative to the working directory
+- run_bash(command): run a shell command in the working directory
+
+## Rules
+- Start by reading README.md
+- Prefer minimal edits. Do not refactor unrelated code.
+- Run the full test suite after each edit to verify.
+"""
+
+USER_PROMPT = "Make the failing tests pass. Begin."
+
+TOOLS = [
+    {
+        "type": "function",
+        "function": {
+            "name": "read_file",
+            "description": "Read a file. Path is relative to the working directory.",
+            "parameters": {
+                "type": "object",
+                "properties": {"path": {"type": "string"}},
+                "required": ["path"],
+            },
+        },
+    },
+    {
+        "type": "function",
+        "function": {
+            "name": "write_file",
+            "description": "Overwrite a file with new content. Path is relative to the working directory.",
+            "parameters": {
+                "type": "object",
+                "properties": {
+                    "path": {"type": "string"},
+                    "content": {"type": "string"},
+                },
+                "required": ["path", "content"],
+            },
+        },
+    },
+    {
+        "type": "function",
+        "function": {
+            "name": "run_bash",
+            "description": "Run a shell command in the working directory. Returns stdout, stderr, and exit code.",
+            "parameters": {
+                "type": "object",
+                "properties": {"command": {"type": "string"}},
+                "required": ["command"],
+            },
+        },
+    },
+]
+
+
+def safe_path(workdir: Path, rel: str) -> Path:
+    p = (workdir / rel).resolve()
+    if not str(p).startswith(str(workdir.resolve())):
+        raise ValueError(f"path escapes workdir: {rel}")
+    return p
+
+
+def tool_read_file(workdir: Path, args: dict) -> str:
+    p = safe_path(workdir, args["path"])
+    if not p.exists():
+        return f"ERROR: {args['path']} does not exist"
+    return p.read_text()
+
+
+def tool_write_file(workdir: Path, args: dict) -> str:
+    p = safe_path(workdir, args["path"])
+    p.parent.mkdir(parents=True, exist_ok=True)
+    p.write_text(args["content"])
+    return f"wrote {args['path']} ({len(args['content'])} bytes)"
+
+
+def tool_run_bash(workdir: Path, args: dict) -> str:
+    try:
+        r = subprocess.run(
+            ["bash", "-c", args["command"]],
+            cwd=workdir,
+            capture_output=True,
+            text=True,
+            timeout=BASH_TIMEOUT_S,
+        )
+    except subprocess.TimeoutExpired:
+        return f"ERROR: command timed out after {BASH_TIMEOUT_S}s"
+    head = (
+        f"exit={r.returncode}\n"
+        f"--- stdout ---\n{r.stdout[-4000:]}\n"
+        f"--- stderr ---\n{r.stderr[-2000:]}"
+    )
+    return head
+
+
+TOOL_DISPATCH = {
+    "read_file": tool_read_file,
+    "write_file": tool_write_file,
+    "run_bash": tool_run_bash,
+}
+
+
+def ollama_chat(model: str, messages: list) -> dict:
+    payload = {
+        "model": model,
+        "messages": messages,
+        "tools": TOOLS,
+        "stream": False,
+        "think": False,
+        "keep_alive": "10m",
+        "options": {
+            "num_ctx": 32768,
+            "num_predict": 4096,
+            "temperature": 0.3,
+        },
+    }
+    data = json.dumps(payload).encode()
+    req = urlreq.Request(
+        f"{OLLAMA_HOST}/api/chat",
+        data=data,
+        headers={"Content-Type": "application/json"},
+    )
+    with urlreq.urlopen(req, timeout=REQUEST_TIMEOUT_S) as resp:
+        return json.loads(resp.read())
+
+
+def pytest_passes(workdir: Path) -> bool:
+    r = subprocess.run(
+        ["python3", "-m", "pytest", "tests/", "-q"],
+        cwd=workdir,
+        capture_output=True,
+        text=True,
+        timeout=60,
+    )
+    return r.returncode == 0
+
+
+def run_bakeoff(model: str, workdir: Path, log_path: Path) -> dict:
+    log_path.parent.mkdir(parents=True, exist_ok=True)
+
+    messages = [
+        {"role": "system", "content": SYSTEM_PROMPT},
+        {"role": "user", "content": USER_PROMPT},
+    ]
+
+    trace = {
+        "model": model,
+        "workdir": str(workdir),
+        "started_at": time.time(),
+        "turns": [],
+        "final": None,
+    }
+
+    tool_call_counts = {"read_file": 0, "write_file": 0, "run_bash": 0}
+    halt_reason = None
+
+    for iteration in range(1, MAX_ITERATIONS + 1):
+        turn_start = time.time()
+        try:
+            response = ollama_chat(model, messages)
+        except Exception as e:
+            halt_reason = f"chat_error: {e}"
+            trace["turns"].append(
+                {"iteration": iteration, "error": str(e), "elapsed_s": time.time() - turn_start}
+            )
+            break
+
+        assistant_msg = response.get("message", {})
+        content = assistant_msg.get("content", "") or ""
+        tool_calls = assistant_msg.get("tool_calls", []) or []
+
+        turn = {
+            "iteration": iteration,
+            "elapsed_s": round(time.time() - turn_start, 2),
+            "content": content,
+            "tool_calls": [],
+            "prompt_eval_count": response.get("prompt_eval_count"),
+            "eval_count": response.get("eval_count"),
+        }
+
+        messages.append({"role": "assistant", "content": content, "tool_calls": tool_calls})
+
+        if not tool_calls:
+            trace["turns"].append(turn)
+            halt_reason = "no_tool_calls"
+            break
+
+        for tc in tool_calls:
+            fn = tc.get("function", {})
+            name = fn.get("name")
+            args = fn.get("arguments") or {}
+            if isinstance(args, str):
+                try:
+                    args = json.loads(args)
+                except Exception:
+                    args = {"_raw": args}
+
+            if name not in TOOL_DISPATCH:
+                result = f"ERROR: unknown tool {name}"
+            else:
+                try:
+                    result = TOOL_DISPATCH[name](workdir, args)
+                    tool_call_counts[name] = tool_call_counts.get(name, 0) + 1
+                except Exception as e:
+                    result = f"ERROR: {e}"
+
+            turn["tool_calls"].append({"name": name, "arguments": args, "result": result[:800]})
+            messages.append({"role": "tool", "content": result})
+
+        trace["turns"].append(turn)
+
+        if iteration == MAX_ITERATIONS:
+            halt_reason = "iteration_cap"
+            break
+
+    final_pass = pytest_passes(workdir)
+    trace["final"] = {
+        "halt_reason": halt_reason,
+        "tests_pass": final_pass,
+        "iterations_used": len(trace["turns"]),
+        "tool_call_counts": tool_call_counts,
+        "wall_clock_s": round(time.time() - trace["started_at"], 2),
+    }
+
+    log_path.write_text(json.dumps(trace, indent=2, default=str))
+    return trace
+
+
+def main():
+    if len(sys.argv) != 4:
+        print(__doc__, file=sys.stderr)
+        sys.exit(2)
+
+    model, workdir_s, log_s = sys.argv[1], sys.argv[2], sys.argv[3]
+    workdir = Path(workdir_s).resolve()
+    log_path = Path(log_s).resolve()
+
+    seed = Path(__file__).parent / "task_seed"
+    if workdir.exists():
+        shutil.rmtree(workdir)
+    shutil.copytree(seed, workdir)
+
+    result = run_bakeoff(model, workdir, log_path)
+    final = result["final"]
+    print(
+        f"model={model}  pass={final['tests_pass']}  "
+        f"iters={final['iterations_used']}  "
+        f"read={final['tool_call_counts'].get('read_file', 0)}  "
+        f"write={final['tool_call_counts'].get('write_file', 0)}  "
+        f"bash={final['tool_call_counts'].get('run_bash', 0)}  "
+        f"halt={final['halt_reason']}  "
+        f"wall={final['wall_clock_s']}s"
+    )
+
+
+if __name__ == "__main__":
+    main()
@@ -0,0 +1,106 @@
+{
+  "model": "gemma4:26b",
+  "workdir": "/home/claude/bin/gemma4-research/scripts/bakeoff/runs/gemma4-26b-retry/work",
+  "started_at": 1776533063.5394974,
+  "turns": [
+    {
+      "iteration": 1,
+      "elapsed_s": 6.72,
+      "content": "",
+      "tool_calls": [
+        {
+          "name": "run_bash",
+          "arguments": {
+            "command": "ls -R"
+          },
+          "result": "exit=0\n--- stdout ---\n.:\ncalc\nREADME.md\ntests\n\n./calc:\n__init__.py\n__pycache__\nstats.py\n\n./calc/__pycache__:\n__init__.cpython-313.pyc\nstats.cpython-313.pyc\n\n./tests:\n__pycache__\ntest_stats.py\n\n./tests/__pycache__:\ntest_stats.cpython-313-pytest-9.0.2.pyc\n\n--- stderr ---\n"
+        }
+      ],
+      "prompt_eval_count": 389,
+      "eval_count": 21
+    },
+    {
+      "iteration": 2,
+      "elapsed_s": 0.64,
+      "content": "",
+      "tool_calls": [
+        {
+          "name": "read_file",
+          "arguments": {
+            "path": "README.md"
+          },
+          "result": "# Bakeoff Task\n\nA tiny Python package (`calc/`) with a statistics module. Run `pytest` from this\ndirectory \u2014 two tests currently fail because `median` returns the upper-middle\nelement instead of averaging the two middle elements on even-length inputs.\n\nYour job: make all tests pass. Do not disable or modify the tests.\n\nAllowed tools:\n- `read_file(path)` \u2014 read a file (relative to this directory)\n- `write_file(path, content)` \u2014 overwrite a file (relative to this directory)\n- `run_bash(command)` \u2014 run a shell command (cwd is this directory)\n\nWhen all tests pass, reply with a short summary of the fix and stop calling tools.\n"
+        }
+      ],
+      "prompt_eval_count": 530,
+      "eval_count": 21
+    },
+    {
+      "iteration": 3,
+      "elapsed_s": 0.66,
+      "content": "",
+      "tool_calls": [
+        {
+          "name": "run_bash",
+          "arguments": {
+            "command": "pytest"
+          },
+          "result": "exit=2\n--- stdout ---\n============================= test session starts ==============================\nplatform linux -- Python 3.13.5, pytest-9.0.2, pluggy-1.6.0\nrootdir: /home/claude/bin/gemma4-research/scripts/bakeoff/runs/gemma4-26b-retry/work\nplugins: asyncio-1.3.0, anyio-4.12.1\nasyncio: mode=Mode.STRICT, debug=False, asyncio_default_fixture_loop_scope=None, asyncio_default_test_loop_scope=function\ncollected 0 items / 1 error\n\n==================================== ERRORS ====================================\n_____________________ ERROR collecting tests/test_stats.py _____________________\nImportError while importing test module '/home/claude/bin/gemma4-research/scripts/bakeoff/runs/gemma4-26b-retry/work/tests/test_stats.py'.\nHint: make sure your test modules/packages have valid Python na"
+        }
+      ],
+      "prompt_eval_count": 711,
+      "eval_count": 19
+    },
+    {
+      "iteration": 4,
+      "elapsed_s": 0.88,
+      "content": "",
+      "tool_calls": [
+        {
+          "name": "run_bash",
+          "arguments": {
+            "command": "export PYTHONPATH=$PYTHONPATH:. && pytest"
+          },
+          "result": "exit=1\n--- stdout ---\n============================= test session starts ==============================\nplatform linux -- Python 3.13.5, pytest-9.0.2, pluggy-1.6.0\nrootdir: /home/claude/bin/gemma4-research/scripts/bakeoff/runs/gemma4-26b-retry/work\nplugins: asyncio-1.3.0, anyio-4.12.1\nasyncio: mode=Mode.STRICT, debug=False, asyncio_default_fixture_loop_scope=None, asyncio_default_test_loop_scope=function\ncollected 7 items\n\ntests/test_stats.py ..FFF..                                              [100%]\n\n=================================== FAILURES ===================================\n_______________________________ test_median_even _______________________________\n\n    def test_median_even():\n>       assert median([1, 2, 3, 4]) == 2.5\nE       assert 3 == 2.5\nE        +  where 3 = median([1, 2,"
+        }
+      ],
+      "prompt_eval_count": 1147,
+      "eval_count": 26
+    },
+    {
+      "iteration": 5,
+      "elapsed_s": 1.12,
+      "content": "",
+      "tool_calls": [
+        {
+          "name": "read_file",
+          "arguments": {
+            "path": "calc/stats.py"
+          },
+          "result": "\"\"\"Basic statistics helpers.\"\"\"\n\n\ndef mean(numbers):\n    \"\"\"Arithmetic mean of a non-empty list.\"\"\"\n    return sum(numbers) / len(numbers)\n\n\ndef median(numbers):\n    \"\"\"Return the median of a list of numbers.\"\"\"\n    s = sorted(numbers)\n    n = len(s)\n    return s[n // 2]\n\n\ndef mode(numbers):\n    \"\"\"Return the most common value. Ties broken by first occurrence.\"\"\"\n    counts = {}\n    for x in numbers:\n        counts[x] = counts.get(x, 0) + 1\n    best = None\n    best_count = -1\n    for x in numbers:\n        if counts[x] > best_count:\n            best = x\n            best_count = counts[x]\n    return best\n\n\ndef variance(numbers):\n    \"\"\"Sample variance (divides by n-1).\"\"\"\n    if len(numbers) < 2:\n        raise ValueError(\"variance requires at least 2 values\")\n    m = mean(numbers)\n    return"
+        }
+      ],
+      "prompt_eval_count": 1786,
+      "eval_count": 23
+    },
+    {
+      "iteration": 6,
+      "elapsed_s": 0.6,
+      "content": "",
+      "tool_calls": [],
+      "prompt_eval_count": 2075,
+      "eval_count": 4
+    }
+  ],
+  "final": {
+    "halt_reason": "no_tool_calls",
+    "tests_pass": false,
+    "iterations_used": 6,
+    "tool_call_counts": {
+      "read_file": 2,
+      "write_file": 0,
+      "run_bash": 3
+    },
+    "wall_clock_s": 11.36
+  }
+}
@@ -0,0 +1,106 @@
+{
+  "model": "gemma4:26b",
+  "workdir": "/home/claude/bin/gemma4-research/scripts/bakeoff/runs/gemma4-26b/work",
+  "started_at": 1776532893.203386,
+  "turns": [
+    {
+      "iteration": 1,
+      "elapsed_s": 5.99,
+      "content": "",
+      "tool_calls": [
+        {
+          "name": "run_bash",
+          "arguments": {
+            "command": "ls -R"
+          },
+          "result": "exit=0\n--- stdout ---\n.:\ncalc\nREADME.md\ntests\n\n./calc:\n__init__.py\n__pycache__\nstats.py\n\n./calc/__pycache__:\n__init__.cpython-313.pyc\nstats.cpython-313.pyc\n\n./tests:\n__pycache__\ntest_stats.py\n\n./tests/__pycache__:\ntest_stats.cpython-313-pytest-9.0.2.pyc\n\n--- stderr ---\n"
+        }
+      ],
+      "prompt_eval_count": 389,
+      "eval_count": 21
+    },
+    {
+      "iteration": 2,
+      "elapsed_s": 0.65,
+      "content": "",
+      "tool_calls": [
+        {
+          "name": "read_file",
+          "arguments": {
+            "path": "README.md"
+          },
+          "result": "# Bakeoff Task\n\nA tiny Python package (`calc/`) with a statistics module. Run `pytest` from this\ndirectory \u2014 two tests currently fail because `median` returns the upper-middle\nelement instead of averaging the two middle elements on even-length inputs.\n\nYour job: make all tests pass. Do not disable or modify the tests.\n\nAllowed tools:\n- `read_file(path)` \u2014 read a file (relative to this directory)\n- `write_file(path, content)` \u2014 overwrite a file (relative to this directory)\n- `run_bash(command)` \u2014 run a shell command (cwd is this directory)\n\nWhen all tests pass, reply with a short summary of the fix and stop calling tools.\n"
+        }
+      ],
+      "prompt_eval_count": 530,
+      "eval_count": 21
+    },
+    {
+      "iteration": 3,
+      "elapsed_s": 0.68,
+      "content": "",
+      "tool_calls": [
+        {
+          "name": "run_bash",
+          "arguments": {
+            "command": "pytest"
+          },
+          "result": "exit=2\n--- stdout ---\n============================= test session starts ==============================\nplatform linux -- Python 3.13.5, pytest-9.0.2, pluggy-1.6.0\nrootdir: /home/claude/bin/gemma4-research/scripts/bakeoff/runs/gemma4-26b/work\nplugins: asyncio-1.3.0, anyio-4.12.1\nasyncio: mode=Mode.STRICT, debug=False, asyncio_default_fixture_loop_scope=None, asyncio_default_test_loop_scope=function\ncollected 0 items / 1 error\n\n==================================== ERRORS ====================================\n_____________________ ERROR collecting tests/test_stats.py _____________________\nImportError while importing test module '/home/claude/bin/gemma4-research/scripts/bakeoff/runs/gemma4-26b/work/tests/test_stats.py'.\nHint: make sure your test modules/packages have valid Python names.\nTraceba"
+        }
+      ],
+      "prompt_eval_count": 711,
+      "eval_count": 19
+    },
+    {
+      "iteration": 4,
+      "elapsed_s": 0.95,
+      "content": "",
+      "tool_calls": [
+        {
+          "name": "run_bash",
+          "arguments": {
+            "command": "export PYTHONPATH=$PYTHONPATH:. && pytest"
+          },
+          "result": "exit=1\n--- stdout ---\n============================= test session starts ==============================\nplatform linux -- Python 3.13.5, pytest-9.0.2, pluggy-1.6.0\nrootdir: /home/claude/bin/gemma4-research/scripts/bakeoff/runs/gemma4-26b/work\nplugins: asyncio-1.3.0, anyio-4.12.1\nasyncio: mode=Mode.STRICT, debug=False, asyncio_default_fixture_loop_scope=None, asyncio_default_test_loop_scope=function\ncollected 7 items\n\ntests/test_stats.py ..FFF..                                              [100%]\n\n=================================== FAILURES ===================================\n_______________________________ test_median_even _______________________________\n\n    def test_median_even():\n>       assert median([1, 2, 3, 4]) == 2.5\nE       assert 3 == 2.5\nE        +  where 3 = median([1, 2, 3, 4]"
+        }
+      ],
+      "prompt_eval_count": 1139,
+      "eval_count": 26
+    },
+    {
+      "iteration": 5,
+      "elapsed_s": 1.28,
+      "content": "",
+      "tool_calls": [
+        {
+          "name": "read_file",
+          "arguments": {
+            "path": "calc/stats.py"
+          },
+          "result": "\"\"\"Basic statistics helpers.\"\"\"\n\n\ndef mean(numbers):\n    \"\"\"Arithmetic mean of a non-empty list.\"\"\"\n    return sum(numbers) / len(numbers)\n\n\ndef median(numbers):\n    \"\"\"Return the median of a list of numbers.\"\"\"\n    s = sorted(numbers)\n    n = len(s)\n    return s[n // 2]\n\n\ndef mode(numbers):\n    \"\"\"Return the most common value. Ties broken by first occurrence.\"\"\"\n    counts = {}\n    for x in numbers:\n        counts[x] = counts.get(x, 0) + 1\n    best = None\n    best_count = -1\n    for x in numbers:\n        if counts[x] > best_count:\n            best = x\n            best_count = counts[x]\n    return best\n\n\ndef variance(numbers):\n    \"\"\"Sample variance (divides by n-1).\"\"\"\n    if len(numbers) < 2:\n        raise ValueError(\"variance requires at least 2 values\")\n    m = mean(numbers)\n    return"
+        }
+      ],
+      "prompt_eval_count": 1775,
+      "eval_count": 23
+    },
+    {
+      "iteration": 6,
+      "elapsed_s": 0.64,
+      "content": "",
+      "tool_calls": [],
+      "prompt_eval_count": 2064,
+      "eval_count": 4
+    }
+  ],
+  "final": {
+    "halt_reason": "no_tool_calls",
+    "tests_pass": false,
+    "iterations_used": 6,
+    "tool_call_counts": {
+      "read_file": 2,
+      "write_file": 0,
+      "run_bash": 3
+    },
+    "wall_clock_s": 10.87
+  }
+}
@@ -0,0 +1,139 @@
+{
+  "model": "gemma4:31b-it-q4_K_M",
+  "workdir": "/home/claude/bin/gemma4-research/scripts/bakeoff/runs/gemma4-31b/work",
+  "started_at": 1776532955.296148,
+  "turns": [
+    {
+      "iteration": 1,
+      "elapsed_s": 15.8,
+      "content": "",
+      "tool_calls": [
+        {
+          "name": "read_file",
+          "arguments": {
+            "path": "README.md"
+          },
+          "result": "# Bakeoff Task\n\nA tiny Python package (`calc/`) with a statistics module. Run `pytest` from this\ndirectory \u2014 two tests currently fail because `median` returns the upper-middle\nelement instead of averaging the two middle elements on even-length inputs.\n\nYour job: make all tests pass. Do not disable or modify the tests.\n\nAllowed tools:\n- `read_file(path)` \u2014 read a file (relative to this directory)\n- `write_file(path, content)` \u2014 overwrite a file (relative to this directory)\n- `run_bash(command)` \u2014 run a shell command (cwd is this directory)\n\nWhen all tests pass, reply with a short summary of the fix and stop calling tools.\n"
+        }
+      ],
+      "prompt_eval_count": 389,
+      "eval_count": 21
+    },
+    {
+      "iteration": 2,
+      "elapsed_s": 1.5,
+      "content": "",
+      "tool_calls": [
+        {
+          "name": "run_bash",
+          "arguments": {
+            "command": "pytest"
+          },
+          "result": "exit=2\n--- stdout ---\n============================= test session starts ==============================\nplatform linux -- Python 3.13.5, pytest-9.0.2, pluggy-1.6.0\nrootdir: /home/claude/bin/gemma4-research/scripts/bakeoff/runs/gemma4-31b/work\nplugins: asyncio-1.3.0, anyio-4.12.1\nasyncio: mode=Mode.STRICT, debug=False, asyncio_default_fixture_loop_scope=None, asyncio_default_test_loop_scope=function\ncollected 0 items / 1 error\n\n==================================== ERRORS ====================================\n_____________________ ERROR collecting tests/test_stats.py _____________________\nImportError while importing test module '/home/claude/bin/gemma4-research/scripts/bakeoff/runs/gemma4-31b/work/tests/test_stats.py'.\nHint: make sure your test modules/packages have valid Python names.\nTraceba"
+        }
+      ],
+      "prompt_eval_count": 570,
+      "eval_count": 19
+    },
+    {
+      "iteration": 3,
+      "elapsed_s": 2.42,
+      "content": "",
+      "tool_calls": [
+        {
+          "name": "run_bash",
+          "arguments": {
+            "command": "ls -R"
+          },
+          "result": "exit=0\n--- stdout ---\n.:\ncalc\nREADME.md\ntests\n\n./calc:\n__init__.py\n__pycache__\nstats.py\n\n./calc/__pycache__:\n__init__.cpython-313.pyc\nstats.cpython-313.pyc\n\n./tests:\n__pycache__\ntest_stats.py\n\n./tests/__pycache__:\ntest_stats.cpython-313-pytest-9.0.2.pyc\n\n--- stderr ---\n"
+        }
+      ],
+      "prompt_eval_count": 998,
+      "eval_count": 21
+    },
+    {
+      "iteration": 4,
+      "elapsed_s": 1.69,
+      "content": "",
+      "tool_calls": [
+        {
+          "name": "run_bash",
+          "arguments": {
+            "command": "export PYTHONPATH=$PYTHONPATH:. && pytest"
+          },
+          "result": "exit=1\n--- stdout ---\n============================= test session starts ==============================\nplatform linux -- Python 3.13.5, pytest-9.0.2, pluggy-1.6.0\nrootdir: /home/claude/bin/gemma4-research/scripts/bakeoff/runs/gemma4-31b/work\nplugins: asyncio-1.3.0, anyio-4.12.1\nasyncio: mode=Mode.STRICT, debug=False, asyncio_default_fixture_loop_scope=None, asyncio_default_test_loop_scope=function\ncollected 7 items\n\ntests/test_stats.py ..FFF..                                              [100%]\n\n=================================== FAILURES ===================================\n_______________________________ test_median_even _______________________________\n\n    def test_median_even():\n>       assert median([1, 2, 3, 4]) == 2.5\nE       assert 3 == 2.5\nE        +  where 3 = median([1, 2, 3, 4]"
+        }
+      ],
+      "prompt_eval_count": 1139,
+      "eval_count": 26
+    },
+    {
+      "iteration": 5,
+      "elapsed_s": 3.27,
+      "content": "",
+      "tool_calls": [
+        {
+          "name": "read_file",
+          "arguments": {
+            "path": "calc/stats.py"
+          },
+          "result": "\"\"\"Basic statistics helpers.\"\"\"\n\n\ndef mean(numbers):\n    \"\"\"Arithmetic mean of a non-empty list.\"\"\"\n    return sum(numbers) / len(numbers)\n\n\ndef median(numbers):\n    \"\"\"Return the median of a list of numbers.\"\"\"\n    s = sorted(numbers)\n    n = len(s)\n    return s[n // 2]\n\n\ndef mode(numbers):\n    \"\"\"Return the most common value. Ties broken by first occurrence.\"\"\"\n    counts = {}\n    for x in numbers:\n        counts[x] = counts.get(x, 0) + 1\n    best = None\n    best_count = -1\n    for x in numbers:\n        if counts[x] > best_count:\n            best = x\n            best_count = counts[x]\n    return best\n\n\ndef variance(numbers):\n    \"\"\"Sample variance (divides by n-1).\"\"\"\n    if len(numbers) < 2:\n        raise ValueError(\"variance requires at least 2 values\")\n    m = mean(numbers)\n    return"
+        }
+      ],
+      "prompt_eval_count": 1775,
+      "eval_count": 23
+    },
+    {
+      "iteration": 6,
+      "elapsed_s": 13.42,
+      "content": "",
+      "tool_calls": [
+        {
+          "name": "write_file",
+          "arguments": {
+            "content": "\"\"\"Basic statistics helpers.\"\"\"\n\n\ndef mean(numbers):\n    \"\"\"Arithmetic mean of a non-empty list.\"\"\"\n    return sum(numbers) / len(numbers)\n\n\ndef median(numbers):\n    \"\"\"Return the median of a list of numbers.\"\"\"\n    s = sorted(numbers)\n    n = len(s)\n    if n % 2 == 1:\n        return s[n // 2]\n    else:\n        return (s[n // 2 - 1] + s[n // 2]) / 2\n\n\ndef mode(numbers):\n    \"\"\"Return the most common value. Ties broken by first occurrence.\"\"\"\n    counts = {}\n    for x in numbers:\n        counts[x] = counts.get(x, 0) + 1\n    best = None\n    best_count = -1\n    for x in numbers:\n        if counts[x] > best_count:\n            best = x\n            best_count = counts[x]\n    return best\n\n\ndef variance(numbers):\n    \"\"\"Sample variance (divides by n-1).\"\"\"\n    if len(numbers) < 2:\n        raise ValueError(\"variance requires at least 2 values\")\n    m = mean(numbers)\n    return sum((x - m) ** 2 for x in numbers) / (len(numbers) - 1)\n",
+            "path": "calc/stats.py"
+          },
+          "result": "wrote calc/stats.py (937 bytes)"
+        }
+      ],
+      "prompt_eval_count": 2064,
+      "eval_count": 330
+    },
+    {
+      "iteration": 7,
+      "elapsed_s": 2.52,
+      "content": "",
+      "tool_calls": [
+        {
+          "name": "run_bash",
+          "arguments": {
+            "command": "export PYTHONPATH=$PYTHONPATH:. && pytest"
+          },
+          "result": "exit=0\n--- stdout ---\n============================= test session starts ==============================\nplatform linux -- Python 3.13.5, pytest-9.0.2, pluggy-1.6.0\nrootdir: /home/claude/bin/gemma4-research/scripts/bakeoff/runs/gemma4-31b/work\nplugins: asyncio-1.3.0, anyio-4.12.1\nasyncio: mode=Mode.STRICT, debug=False, asyncio_default_fixture_loop_scope=None, asyncio_default_test_loop_scope=function\ncollected 7 items\n\ntests/test_stats.py .......                                              [100%]\n\n============================== 7 passed in 0.01s ===============================\n\n--- stderr ---\n"
+        }
+      ],
+      "prompt_eval_count": 2411,
+      "eval_count": 27
+    },
+    {
+      "iteration": 8,
+      "elapsed_s": 2.49,
+      "content": "I updated the `median` function in `calc/stats.py` to correctly calculate the average of the two middle elements when the input list has an even number of elements.",
+      "tool_calls": [],
+      "prompt_eval_count": 2622,
+      "eval_count": 41
+    }
+  ],
+  "final": {
+    "halt_reason": "no_tool_calls",
+    "tests_pass": true,
+    "iterations_used": 8,
+    "tool_call_counts": {
+      "read_file": 2,
+      "write_file": 1,
+      "run_bash": 4
+    },
+    "wall_clock_s": 44.06
+  }
+}
@@ -0,0 +1,251 @@
+{
+  "model": "qwen3-coder:30b",
+  "workdir": "/home/claude/bin/gemma4-research/scripts/bakeoff/runs/qwen3-coder-30b/work",
+  "started_at": 1776533012.2470767,
+  "turns": [
+    {
+      "iteration": 1,
+      "elapsed_s": 10.69,
+      "content": "I'll help you make the failing tests pass. First, let's understand what we're working with by reading the README.md file to get context about the project.",
+      "tool_calls": [
+        {
+          "name": "read_file",
+          "arguments": {
+            "path": "README.md"
+          },
+          "result": "# Bakeoff Task\n\nA tiny Python package (`calc/`) with a statistics module. Run `pytest` from this\ndirectory \u2014 two tests currently fail because `median` returns the upper-middle\nelement instead of averaging the two middle elements on even-length inputs.\n\nYour job: make all tests pass. Do not disable or modify the tests.\n\nAllowed tools:\n- `read_file(path)` \u2014 read a file (relative to this directory)\n- `write_file(path, content)` \u2014 overwrite a file (relative to this directory)\n- `run_bash(command)` \u2014 run a shell command (cwd is this directory)\n\nWhen all tests pass, reply with a short summary of the fix and stop calling tools.\n"
+        }
+      ],
+      "prompt_eval_count": 625,
+      "eval_count": 55
+    },
+    {
+      "iteration": 2,
+      "elapsed_s": 0.42,
+      "content": "Now let's look at the test file to understand what's failing:",
+      "tool_calls": [
+        {
+          "name": "read_file",
+          "arguments": {
+            "path": "test_calc.py"
+          },
+          "result": "ERROR: test_calc.py does not exist"
+        }
+      ],
+      "prompt_eval_count": 834,
+      "eval_count": 37
+    },
+    {
+      "iteration": 3,
+      "elapsed_s": 0.36,
+      "content": "Let me check what files are available in the directory:",
+      "tool_calls": [
+        {
+          "name": "run_bash",
+          "arguments": {
+            "command": "ls -la"
+          },
+          "result": "exit=0\n--- stdout ---\ntotal 24\ndrwxrwxr-x 5 claude claude 4096 Apr 18 13:19 .\ndrwxrwxr-x 3 claude claude 4096 Apr 18 13:23 ..\ndrwxrwxr-x 3 claude claude 4096 Apr 18 13:19 calc\ndrwxrwxr-x 3 claude claude 4096 Apr 18 13:19 .pytest_cache\n-rw-rw-r-- 1 claude claude  637 Apr 18 13:19 README.md\ndrwxrwxr-x 3 claude claude 4096 Apr 18 13:20 tests\n\n--- stderr ---\n"
+        }
+      ],
+      "prompt_eval_count": 892,
+      "eval_count": 37
+    },
+    {
+      "iteration": 4,
+      "elapsed_s": 0.35,
+      "content": "",
+      "tool_calls": [
+        {
+          "name": "run_bash",
+          "arguments": {
+            "command": "ls -la tests/"
+          },
+          "result": "exit=0\n--- stdout ---\ntotal 16\ndrwxrwxr-x 3 claude claude 4096 Apr 18 13:20 .\ndrwxrwxr-x 5 claude claude 4096 Apr 18 13:19 ..\ndrwxrwxr-x 2 claude claude 4096 Apr 18 13:20 __pycache__\n-rw-rw-r-- 1 claude claude  591 Apr 18 13:20 test_stats.py\n\n--- stderr ---\n"
+        }
+      ],
+      "prompt_eval_count": 1132,
+      "eval_count": 27
+    },
+    {
+      "iteration": 5,
+      "elapsed_s": 0.41,
+      "content": "",
+      "tool_calls": [
+        {
+          "name": "read_file",
+          "arguments": {
+            "path": "tests/test_stats.py"
+          },
+          "result": "from calc.stats import mean, median, mode, variance\n\n\ndef test_mean_basic():\n    assert mean([1, 2, 3, 4, 5]) == 3.0\n\n\ndef test_median_odd():\n    assert median([1, 2, 3]) == 2\n\n\ndef test_median_even():\n    assert median([1, 2, 3, 4]) == 2.5\n\n\ndef test_median_unsorted():\n    assert median([3, 1, 4, 1, 5, 9, 2, 6]) == 3.5\n\n\ndef test_median_floats():\n    assert median([1.0, 2.0, 3.0, 4.0]) == 2.5\n\n\ndef test_mode_basic():\n    assert mode([1, 2, 2, 3]) == 2\n\n\ndef test_variance_basic():\n    # sample variance (n-1) of [1, 2, 3, 4, 5] is 10/4 = 2.5\n    assert variance([1, 2, 3, 4, 5]) == 2.5\n"
+        }
+      ],
+      "prompt_eval_count": 1305,
+      "eval_count": 24
+    },
+    {
+      "iteration": 6,
+      "elapsed_s": 0.43,
+      "content": "Now let's look at the calc module to see the current implementation:",
+      "tool_calls": [
+        {
+          "name": "read_file",
+          "arguments": {
+            "path": "calc"
+          },
+          "result": "ERROR: [Errno 21] Is a directory: '/home/claude/bin/gemma4-research/scripts/bakeoff/runs/qwen3-coder-30b/work/calc'"
+        }
+      ],
+      "prompt_eval_count": 1593,
+      "eval_count": 35
+    },
+    {
+      "iteration": 7,
+      "elapsed_s": 0.33,
+      "content": "",
+      "tool_calls": [
+        {
+          "name": "run_bash",
+          "arguments": {
+            "command": "ls -la calc/"
+          },
+          "result": "exit=0\n--- stdout ---\ntotal 16\ndrwxrwxr-x 3 claude claude 4096 Apr 18 13:19 .\ndrwxrwxr-x 5 claude claude 4096 Apr 18 13:19 ..\n-rw-rw-r-- 1 claude claude    0 Apr 18 13:19 __init__.py\ndrwxrwxr-x 2 claude claude 4096 Apr 18 13:19 __pycache__\n-rw-rw-r-- 1 claude claude  857 Apr 18 13:19 stats.py\n\n--- stderr ---\n"
+        }
+      ],
+      "prompt_eval_count": 1683,
+      "eval_count": 27
+    },
+    {
+      "iteration": 8,
+      "elapsed_s": 0.33,
+      "content": "",
+      "tool_calls": [
+        {
+          "name": "read_file",
+          "arguments": {
+            "path": "calc/stats.py"
+          },
+          "result": "\"\"\"Basic statistics helpers.\"\"\"\n\n\ndef mean(numbers):\n    \"\"\"Arithmetic mean of a non-empty list.\"\"\"\n    return sum(numbers) / len(numbers)\n\n\ndef median(numbers):\n    \"\"\"Return the median of a list of numbers.\"\"\"\n    s = sorted(numbers)\n    n = len(s)\n    return s[n // 2]\n\n\ndef mode(numbers):\n    \"\"\"Return the most common value. Ties broken by first occurrence.\"\"\"\n    counts = {}\n    for x in numbers:\n        counts[x] = counts.get(x, 0) + 1\n    best = None\n    best_count = -1\n    for x in numbers:\n        if counts[x] > best_count:\n            best = x\n            best_count = counts[x]\n    return best\n\n\ndef variance(numbers):\n    \"\"\"Sample variance (divides by n-1).\"\"\"\n    if len(numbers) < 2:\n        raise ValueError(\"variance requires at least 2 values\")\n    m = mean(numbers)\n    return"
+        }
+      ],
+      "prompt_eval_count": 1885,
+      "eval_count": 23
+    },
+    {
+      "iteration": 9,
+      "elapsed_s": 1.32,
+      "content": "Now I understand the issue. Looking at the failing tests, specifically `test_median_even()` and `test_median_unsorted()`, I can see that the median function is returning the upper-middle element instead of averaging the two middle elements for even-length lists.\n\nIn the current implementation:\n- For `[1, 2, 3, 4]`, it returns `s[4 // 2]` = `s[2]` = `3` (upper-middle)\n- But it should return `(2 + 3) / 2` = `2.5` (average of two middle elements)\n\nLet me run the tests first to confirm the current failures:",
+      "tool_calls": [
+        {
+          "name": "run_bash",
+          "arguments": {
+            "command": "pytest -v"
+          },
+          "result": "exit=2\n--- stdout ---\n============================= test session starts ==============================\nplatform linux -- Python 3.13.5, pytest-9.0.2, pluggy-1.6.0 -- /usr/bin/python3\ncachedir: .pytest_cache\nrootdir: /home/claude/bin/gemma4-research/scripts/bakeoff/runs/qwen3-coder-30b/work\nplugins: asyncio-1.3.0, anyio-4.12.1\nasyncio: mode=Mode.STRICT, debug=False, asyncio_default_fixture_loop_scope=None, asyncio_default_test_loop_scope=function\ncollecting ... collected 0 items / 1 error\n\n==================================== ERRORS ====================================\n_____________________ ERROR collecting tests/test_stats.py _____________________\nImportError while importing test module '/home/claude/bin/gemma4-research/scripts/bakeoff/runs/qwen3-coder-30b/work/tests/test_stats.py'.\nHint: "
+        }
+      ],
+      "prompt_eval_count": 2143,
+      "eval_count": 163
+    },
+    {
+      "iteration": 10,
+      "elapsed_s": 0.61,
+      "content": "I need to run the tests from the correct directory. Let me check the current working directory and run pytest properly:",
+      "tool_calls": [
+        {
+          "name": "run_bash",
+          "arguments": {
+            "command": "pwd && python -m pytest tests/ -v"
+          },
+          "result": "exit=127\n--- stdout ---\n/home/claude/bin/gemma4-research/scripts/bakeoff/runs/qwen3-coder-30b/work\n\n--- stderr ---\nbash: line 1: python: command not found\n"
+        }
+      ],
+      "prompt_eval_count": 2693,
+      "eval_count": 56
+    },
+    {
+      "iteration": 11,
+      "elapsed_s": 0.39,
+      "content": "",
+      "tool_calls": [
+        {
+          "name": "run_bash",
+          "arguments": {
+            "command": "pwd && python3 -m pytest tests/ -v"
+          },
+          "result": "exit=1\n--- stdout ---\n/home/claude/bin/gemma4-research/scripts/bakeoff/runs/qwen3-coder-30b/work\n============================= test session starts ==============================\nplatform linux -- Python 3.13.5, pytest-9.0.2, pluggy-1.6.0 -- /usr/bin/python3\ncachedir: .pytest_cache\nrootdir: /home/claude/bin/gemma4-research/scripts/bakeoff/runs/qwen3-coder-30b/work\nplugins: asyncio-1.3.0, anyio-4.12.1\nasyncio: mode=Mode.STRICT, debug=False, asyncio_default_fixture_loop_scope=None, asyncio_default_test_loop_scope=function\ncollecting ... collected 7 items\n\ntests/test_stats.py::test_mean_basic PASSED                              [ 14%]\ntests/test_stats.py::test_median_odd PASSED                              [ 28%]\ntests/test_stats.py::test_median_even FAILED                             [ 42%]\nt"
+        }
+      ],
+      "prompt_eval_count": 2812,
+      "eval_count": 34
+    },
+    {
+      "iteration": 12,
+      "elapsed_s": 3.11,
+      "content": "Perfect! Now I can see the exact failures. The issue is in the `median` function in `calc/stats.py`. For even-length lists, it should return the average of the two middle elements, but currently it's just returning the upper-middle element.\n\nLet me fix the median function:",
+      "tool_calls": [
+        {
+          "name": "write_file",
+          "arguments": {
+            "path": "calc/stats.py",
+            "content": "\"\"\"Basic statistics helpers.\"\"\"\n\n\ndef mean(numbers):\n    \"\"\"Arithmetic mean of a non-empty list.\"\"\"\n    return sum(numbers) / len(numbers)\n\n\ndef median(numbers):\n    \"\"\"Return the median of a list of numbers.\"\"\"\n    s = sorted(numbers)\n    n = len(s)\n    if n % 2 == 1:\n        # Odd length: return the middle element\n        return s[n // 2]\n    else:\n        # Even length: return the average of the two middle elements\n        mid1 = s[n // 2 - 1]\n        mid2 = s[n // 2]\n        return (mid1 + mid2) / 2\n\n\ndef mode(numbers):\n    \"\"\"Return the most common value. Ties broken by first occurrence.\"\"\"\n    counts = {}\n    for x in numbers:\n        counts[x] = counts.get(x, 0) + 1\n    best = None\n    best_count = -1\n    for x in numbers:\n        if counts[x] > best_count:\n            best = x\n            best_count = counts[x]\n    return best\n\n\ndef variance(numbers):\n    \"\"\"Sample variance (divides by n-1).\"\"\"\n    if len(numbers) < 2:\n        raise ValueError(\"variance requires at least 2 values\")\n    m = mean(numbers)\n    return sum((x - m) ** 2 for x in numbers) / (len(numbers) - 1)"
+          },
+          "result": "wrote calc/stats.py (1093 bytes)"
+        }
+      ],
+      "prompt_eval_count": 3563,
+      "eval_count": 387
+    },
+    {
+      "iteration": 13,
+      "elapsed_s": 0.44,
+      "content": "Now let's run the tests to see if they pass:",
+      "tool_calls": [
+        {
+          "name": "run_bash",
+          "arguments": {
+            "command": "python3 -m pytest tests/ -v"
+          },
+          "result": "exit=0\n--- stdout ---\n============================= test session starts ==============================\nplatform linux -- Python 3.13.5, pytest-9.0.2, pluggy-1.6.0 -- /usr/bin/python3\ncachedir: .pytest_cache\nrootdir: /home/claude/bin/gemma4-research/scripts/bakeoff/runs/qwen3-coder-30b/work\nplugins: asyncio-1.3.0, anyio-4.12.1\nasyncio: mode=Mode.STRICT, debug=False, asyncio_default_fixture_loop_scope=None, asyncio_default_test_loop_scope=function\ncollecting ... collected 7 items\n\ntests/test_stats.py::test_mean_basic PASSED                              [ 14%]\ntests/test_stats.py::test_median_odd PASSED                              [ 28%]\ntests/test_stats.py::test_median_even PASSED                             [ 42%]\ntests/test_stats.py::test_median_unsorted PASSED                         [ 5"
+        }
+      ],
+      "prompt_eval_count": 3974,
+      "eval_count": 44
+    },
+    {
+      "iteration": 14,
+      "elapsed_s": 1.75,
+      "content": "Perfect! All tests are now passing. Let me summarize what I did to fix the issue:\n\nI fixed the `median` function in `calc/stats.py` to properly handle even-length lists. The original implementation was returning just the upper-middle element for even-length lists, but according to statistical convention and the test expectations, it should return the average of the two middle elements. My fix checks if the list length is odd or even, and for even lengths, it calculates the average of the two middle elements correctly.\n\nThe fix involved modifying the median function to:\n1. Sort the input list\n2. Check if the length is odd or even\n3. For odd lengths, return the middle element (as before)\n4. For even lengths, return the average of the two middle elements\n\nThis ensures that all the median tests now pass correctly.",
+      "tool_calls": [
+        {
+          "name": "run_bash",
+          "arguments": {
+            "command": "echo \"All tests pass - median function now correctly handles even-length lists by averaging the two middle elements\""
+          },
+          "result": "exit=0\n--- stdout ---\nAll tests pass - median function now correctly handles even-length lists by averaging the two middle elements\n\n--- stderr ---\n"
+        }
+      ],
+      "prompt_eval_count": 4319,
+      "eval_count": 213
+    },
+    {
+      "iteration": 15,
+      "elapsed_s": 0.65,
+      "content": "I've successfully fixed the failing tests by correcting the median function in `calc/stats.py`. The issue was that for even-length lists, the median function was returning the upper-middle element instead of averaging the two middle elements. I modified the function to properly handle both odd and even-length lists, ensuring all tests now pass.",
+      "tool_calls": [],
+      "prompt_eval_count": 4574,
+      "eval_count": 66
+    }
+  ],
+  "final": {
+    "halt_reason": "no_tool_calls",
+    "tests_pass": true,
+    "iterations_used": 15,
+    "tool_call_counts": {
+      "read_file": 4,
+      "write_file": 1,
+      "run_bash": 8
+    },
+    "wall_clock_s": 22.58
+  }
+}
@@ -0,0 +1,14 @@
+# Bakeoff Task
+
+A tiny Python package (`calc/`) with a statistics module. Run `pytest` from this
+directory — two tests currently fail because `median` returns the upper-middle
+element instead of averaging the two middle elements on even-length inputs.
+
+Your job: make all tests pass. Do not disable or modify the tests.
+
+Allowed tools:
+- `read_file(path)` — read a file (relative to this directory)
+- `write_file(path, content)` — overwrite a file (relative to this directory)
+- `run_bash(command)` — run a shell command (cwd is this directory)
+
+When all tests pass, reply with a short summary of the fix and stop calling tools.
@@ -0,0 +1,35 @@
+"""Basic statistics helpers."""
+
+
+def mean(numbers):
+    """Arithmetic mean of a non-empty list."""
+    return sum(numbers) / len(numbers)
+
+
+def median(numbers):
+    """Return the median of a list of numbers."""
+    s = sorted(numbers)
+    n = len(s)
+    return s[n // 2]
+
+
+def mode(numbers):
+    """Return the most common value. Ties broken by first occurrence."""
+    counts = {}
+    for x in numbers:
+        counts[x] = counts.get(x, 0) + 1
+    best = None
+    best_count = -1
+    for x in numbers:
+        if counts[x] > best_count:
+            best = x
+            best_count = counts[x]
+    return best
+
+
+def variance(numbers):
+    """Sample variance (divides by n-1)."""
+    if len(numbers) < 2:
+        raise ValueError("variance requires at least 2 values")
+    m = mean(numbers)
+    return sum((x - m) ** 2 for x in numbers) / (len(numbers) - 1)
@@ -0,0 +1,30 @@
+from calc.stats import mean, median, mode, variance
+
+
+def test_mean_basic():
+    assert mean([1, 2, 3, 4, 5]) == 3.0
+
+
+def test_median_odd():
+    assert median([1, 2, 3]) == 2
+
+
+def test_median_even():
+    assert median([1, 2, 3, 4]) == 2.5
+
+
+def test_median_unsorted():
+    assert median([3, 1, 4, 1, 5, 9, 2, 6]) == 3.5
+
+
+def test_median_floats():
+    assert median([1.0, 2.0, 3.0, 4.0]) == 2.5
+
+
+def test_mode_basic():
+    assert mode([1, 2, 2, 3]) == 2
+
+
+def test_variance_basic():
+    # sample variance (n-1) of [1, 2, 3, 4, 5] is 10/4 = 2.5
+    assert variance([1, 2, 3, 4, 5]) == 2.5