Add regression tests for tool_calls assignment in assistant message

Tests verify that:
- tool_calls is present and correctly assigned when LLM returns tool calls
- tool_calls key is absent when LLM returns no tool calls
- Multiple tool calls are all correctly assigned
- Content field is preserved regardless of tool_calls presence

Guards against regression of the bug fixed in 99c1873 where tool_calls
was always included in the assistant message dict even when empty.

Co-Authored-By: Nataly Andries <patrinat@gmail.com>

01-tools/tests/__init__.py

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+

01-tools/tests/test_agent.py

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+"""Regression tests for AgentSession.chat() tool_calls assignment.
+
+Tests that 'tool_calls' is only present in the assistant message when the LLM
+actually returns tool calls, and that the value is correctly assigned when present.
+This guards against the bug fixed in commit 99c1873 where 'tool_calls' was always
+included in the assistant message dict (even as an empty list), which could cause
+issues with LLM providers that reject empty tool_calls.
+"""
+
+import json
+import pytest
+from unittest.mock import AsyncMock, MagicMock, patch
+from dataclasses import dataclass
+
+from mybot.core.agent import Agent, AgentSession
+from mybot.core.session_state import SessionState
+from mybot.provider.llm import LLMToolCall
+from mybot.tools.registry import ToolRegistry
+
+
+@dataclass
+class FakeAgentDef:
+    """Minimal stand-in for AgentDef used by SessionState.build_messages."""
+    agent_md: str = "You are a test agent."
+    llm: MagicMock = None
+
+    def __post_init__(self):
+        if self.llm is None:
+            self.llm = MagicMock()
+
+
+def _make_session(llm_mock: AsyncMock) -> AgentSession:
+    """Create an AgentSession wired to a mocked LLM provider."""
+    agent = MagicMock(spec=Agent)
+    agent.agent_def = FakeAgentDef()
+    agent.llm = llm_mock
+
+    state = SessionState(
+        session_id="test-session",
+        agent=agent,
+        messages=[],
+    )
+
+    tools = ToolRegistry()
+    return AgentSession(agent=agent, state=state, tools=tools)
+
+
+@pytest.mark.asyncio
+async def test_tool_calls_present_when_llm_returns_tool_calls():
+    """When the LLM returns tool calls, 'tool_calls' must be in the assistant message."""
+    tool_call = LLMToolCall(
+        id="call_123",
+        name="read_file",
+        arguments=json.dumps({"path": "/tmp/test.txt"}),
+    )
+
+    llm_mock = AsyncMock()
+    # First call: LLM returns a tool call
+    llm_mock.chat = AsyncMock(
+        side_effect=[
+            ("Using tool...", [tool_call]),
+            ("Here is the result.", []),
+        ]
+    )
+
+    session = _make_session(llm_mock)
+    # Mock the tool execution so _handle_tool_calls completes
+    session.tools.execute_tool = AsyncMock(return_value="file contents")
+
+    await session.chat("read the file")
+
+    # Find the first assistant message (the one with tool calls)
+    assistant_msgs = [m for m in session.state.messages if m["role"] == "assistant"]
+    assert len(assistant_msgs) == 2
+
+    first_assistant = assistant_msgs[0]
+    assert "tool_calls" in first_assistant, (
+        "assistant message must contain 'tool_calls' when the LLM returns tool calls"
+    )
+    assert len(first_assistant["tool_calls"]) == 1
+
+    tc = first_assistant["tool_calls"][0]
+    assert tc["id"] == "call_123"
+    assert tc["type"] == "function"
+    assert tc["function"]["name"] == "read_file"
+    assert tc["function"]["arguments"] == json.dumps({"path": "/tmp/test.txt"})
+
+
+@pytest.mark.asyncio
+async def test_tool_calls_absent_when_llm_returns_no_tool_calls():
+    """When the LLM returns no tool calls, 'tool_calls' must NOT be in the assistant message."""
+    llm_mock = AsyncMock()
+    llm_mock.chat = AsyncMock(return_value=("Hello! How can I help?", []))
+
+    session = _make_session(llm_mock)
+
+    await session.chat("hi")
+
+    assistant_msgs = [m for m in session.state.messages if m["role"] == "assistant"]
+    assert len(assistant_msgs) == 1
+
+    assistant_msg = assistant_msgs[0]
+    assert "tool_calls" not in assistant_msg, (
+        "assistant message must NOT contain 'tool_calls' when the LLM returns no tool calls"
+    )
+
+
+@pytest.mark.asyncio
+async def test_tool_calls_correct_with_multiple_tool_calls():
+    """When the LLM returns multiple tool calls, all are correctly assigned."""
+    tool_calls = [
+        LLMToolCall(id="call_1", name="read_file", arguments=json.dumps({"path": "a.txt"})),
+        LLMToolCall(id="call_2", name="bash", arguments=json.dumps({"command": "ls"})),
+    ]
+
+    llm_mock = AsyncMock()
+    llm_mock.chat = AsyncMock(
+        side_effect=[
+            ("Running tools...", tool_calls),
+            ("Done.", []),
+        ]
+    )
+
+    session = _make_session(llm_mock)
+    session.tools.execute_tool = AsyncMock(return_value="ok")
+
+    await session.chat("do stuff")
+
+    assistant_msgs = [m for m in session.state.messages if m["role"] == "assistant"]
+    first_assistant = assistant_msgs[0]
+
+    assert "tool_calls" in first_assistant
+    assert len(first_assistant["tool_calls"]) == 2
+    assert first_assistant["tool_calls"][0]["id"] == "call_1"
+    assert first_assistant["tool_calls"][0]["function"]["name"] == "read_file"
+    assert first_assistant["tool_calls"][1]["id"] == "call_2"
+    assert first_assistant["tool_calls"][1]["function"]["name"] == "bash"
+
+
+@pytest.mark.asyncio
+async def test_assistant_message_content_preserved_regardless_of_tool_calls():
+    """Content field is always set correctly, with or without tool calls."""
+    tool_call = LLMToolCall(
+        id="call_x", name="bash", arguments=json.dumps({"command": "echo hi"}),
+    )
+
+    llm_mock = AsyncMock()
+    llm_mock.chat = AsyncMock(
+        side_effect=[
+            ("Thinking...", [tool_call]),
+            ("Final answer.", []),
+        ]
+    )
+
+    session = _make_session(llm_mock)
+    session.tools.execute_tool = AsyncMock(return_value="hi")
+
+    result = await session.chat("say hi")
+
+    assistant_msgs = [m for m in session.state.messages if m["role"] == "assistant"]
+
+    # First assistant message (with tool call)
+    assert assistant_msgs[0]["content"] == "Thinking..."
+    assert "tool_calls" in assistant_msgs[0]
+
+    # Second assistant message (no tool call)
+    assert assistant_msgs[1]["content"] == "Final answer."
+    assert "tool_calls" not in assistant_msgs[1]
+
+    assert result == "Final answer."