vllm/tests/entrypoints/test_context.py

# SPDX-License-Identifier: Apache-2.0
# SPDX-FileCopyrightText: Copyright contributors to the vLLM project

from unittest.mock import MagicMock, patch

import pytest
from openai_harmony import Author, Message, Role, StreamState, TextContent

from vllm.entrypoints.openai.responses.context import (
    HarmonyContext,
    SimpleContext,
    StreamingHarmonyContext,
    TurnMetrics,
)
from vllm.outputs import CompletionOutput, RequestOutput


def create_mock_request_output(
    prompt_token_ids=None,
    output_token_ids=None,
    num_cached_tokens=0,
    finished=True,
):
    """Helper function to create a mock RequestOutput object for testing."""
    outputs = []
    token_ids = output_token_ids if output_token_ids is not None else []
    outputs = [
        CompletionOutput(
            index=0,
            text="Test output",
            token_ids=token_ids,
            cumulative_logprob=0.0,
            logprobs=None,
            finish_reason=None,
            stop_reason=None,
        )
    ]

    return RequestOutput(
        request_id="test-id",
        prompt="Test prompt",
        prompt_token_ids=prompt_token_ids,
        prompt_logprobs=None,
        outputs=outputs,
        finished=finished,
        num_cached_tokens=num_cached_tokens,
    )


async def generate_mock_outputs(
    num_turns, prompt_token_counts, output_token_counts, cached_token_counts=None
):
    """Generate a sequence of mock RequestOutput objects to simulate multiple
    turns."""
    if cached_token_counts is None:
        cached_token_counts = [0] * num_turns

    for i in range(num_turns):
        # Create mock prompt token IDs and output token IDs
        prompt_token_ids = list(range(1, prompt_token_counts[i] + 1))
        output_token_ids = list(range(1, output_token_counts[i] + 1))

        # Create and yield the RequestOutput
        yield create_mock_request_output(
            prompt_token_ids=prompt_token_ids,
            output_token_ids=output_token_ids,
            num_cached_tokens=cached_token_counts[i],
        )


@pytest.fixture
def mock_parser():
    """Set up a mock parser for tests."""
    with patch(
        "vllm.entrypoints.openai.responses.context.get_streamable_parser_for_assistant"
    ) as mock_parser_factory:
        # Create a mock parser object
        parser = MagicMock()
        parser.messages = []
        parser.current_channel = None
        parser.state = StreamState.EXPECT_START
        mock_parser_factory.return_value = parser
        yield parser


def test_single_turn_token_counting():
    """Test token counting behavior for a single turn."""
    # Create a context
    context = HarmonyContext(messages=[], available_tools=[])

    # Create a mock RequestOutput with specific token counts
    mock_output = create_mock_request_output(
        prompt_token_ids=[1, 2, 3, 4, 5],  # 5 prompt tokens
        output_token_ids=[6, 7, 8],  # 3 output tokens
        num_cached_tokens=2,  # 2 cached tokens
    )

    # Append the output to the context
    context.append_output(mock_output)

    # Verify the token counts
    assert context.num_prompt_tokens == 5
    assert context.num_output_tokens == 3
    assert context.num_cached_tokens == 2
    assert context.num_tool_output_tokens == 0  # No tool tokens in first turn

    # Verify internal state tracking
    assert not context.is_first_turn
    assert len(context.all_turn_metrics) == 1
    previous_turn = context.all_turn_metrics[0]
    assert previous_turn.input_tokens == 5
    assert previous_turn.output_tokens == 3
    assert previous_turn.cached_input_tokens == 2
    assert previous_turn.tool_output_tokens == 0


@pytest.mark.asyncio
async def test_multi_turn_token_counting():
    """Test token counting behavior across multiple turns with tool output."""
    # Create a context
    context = HarmonyContext(messages=[], available_tools=["browser"])

    # Simulate a conversation with 3 turns
    # Turn 1: prefill 5, decode 3, tool 7
    # Turn 2: prefill 15, cached 5, decode 4, tool 1
    # Turn 3: prefill 20, cached 15, decode 5
    prompt_token_counts = [5, 15, 20]
    output_token_counts = [3, 4, 5]
    cached_token_counts = [0, 5, 15]
    mock_generator = generate_mock_outputs(
        3, prompt_token_counts, output_token_counts, cached_token_counts
    )

    # First turn - initial prompt and response
    mock_output1 = await anext(mock_generator)
    context.append_output(mock_output1)

    # At this point, we should have 5 prompt tokens and 3 output tokens
    assert context.num_prompt_tokens == 5
    assert context.num_output_tokens == 3
    assert context.num_tool_output_tokens == 0

    # Second turn - after tool output
    mock_output2 = await anext(mock_generator)
    context.append_output(mock_output2)
    # Current prompt tokens (15) - last_turn_input_tokens (5) -
    # last_turn_output_tokens (3) = 7
    expected_tool_output = 7

    assert context.num_prompt_tokens == 5 + 15
    assert context.num_output_tokens == 3 + 4
    assert context.num_tool_output_tokens == expected_tool_output
    assert context.num_cached_tokens == 5

    # Third turn - final response
    mock_output3 = await anext(mock_generator)
    context.append_output(mock_output3)
    # Additional tool output tokens from third turn:
    # Current prompt (20) - last_turn_input_tokens (15) -
    # last_turn_output_tokens (4) = 1
    expected_tool_output = 7 + 1

    assert context.num_prompt_tokens == 5 + 15 + 20
    assert context.num_output_tokens == 3 + 4 + 5
    assert context.num_tool_output_tokens == expected_tool_output
    assert context.num_cached_tokens == 5 + 15

    # Validate all turn metrics
    assert len(context.all_turn_metrics) == 3
    for i, turn in enumerate(context.all_turn_metrics):
        assert turn.input_tokens == prompt_token_counts[i]
        assert turn.output_tokens == output_token_counts[i]
        assert turn.cached_input_tokens == cached_token_counts[i]
    assert context.all_turn_metrics[1].tool_output_tokens == 7
    assert context.all_turn_metrics[2].tool_output_tokens == 1


def test_empty_output_tokens():
    """Test behavior when RequestOutput has empty output tokens."""
    context = HarmonyContext(messages=[], available_tools=[])

    # Create a RequestOutput with empty output tokens
    mock_output = create_mock_request_output(
        prompt_token_ids=[1, 2, 3],  # 3 prompt tokens
        output_token_ids=[],  # Empty output tokens list
        num_cached_tokens=1,
    )

    context.append_output(mock_output)

    # Should handle empty outputs gracefully
    assert context.num_prompt_tokens == 3
    assert context.num_output_tokens == 0  # No output tokens
    assert context.num_cached_tokens == 1
    assert context.num_tool_output_tokens == 0


def test_missing_prompt_token_ids():
    """Test behavior when RequestOutput has None prompt_token_ids."""
    context = HarmonyContext(messages=[], available_tools=[])

    mock_output = create_mock_request_output(
        prompt_token_ids=None,  # No prompt token IDs
        output_token_ids=[1, 2],  # 2 output tokens
        num_cached_tokens=0,
    )

    # Logger.error will be called, but we don't need to check for warnings
    # here Just ensure it doesn't raise an exception
    context.append_output(mock_output)

    # Should handle missing prompt tokens gracefully
    assert context.num_prompt_tokens == 0
    assert context.num_output_tokens == 2
    assert context.num_cached_tokens == 0
    assert context.num_tool_output_tokens == 0


def test_reasoning_tokens_counting(mock_parser):
    """Test that reasoning tokens are counted correctly."""
    context = HarmonyContext(messages=[], available_tools=[])

    # Mock parser to simulate reasoning channel
    mock_parser.current_channel = "analysis"  # Reasoning channel

    mock_output = create_mock_request_output(
        prompt_token_ids=[1, 2, 3],
        output_token_ids=[4, 5, 6, 7],  # 4 tokens, all in reasoning
        num_cached_tokens=0,
    )

    context.append_output(mock_output)

    # All output tokens should be counted as reasoning
    assert context.num_reasoning_tokens == 4
    assert context.num_output_tokens == 4


def test_preamble_tokens_not_counted_as_reasoning(mock_parser):
    """Preambles (commentary with no recipient) are visible user text,
    not hidden reasoning. They must NOT inflate num_reasoning_tokens."""
    context = HarmonyContext(messages=[], available_tools=[])

    mock_parser.current_channel = "commentary"
    mock_parser.current_recipient = None  # preamble

    mock_output = create_mock_request_output(
        prompt_token_ids=[1, 2, 3],
        output_token_ids=[4, 5, 6],
        num_cached_tokens=0,
    )
    context.append_output(mock_output)

    assert context.num_reasoning_tokens == 0
    assert context.num_output_tokens == 3


def test_commentary_with_recipient_counted_as_reasoning(mock_parser):
    """Commentary directed at a tool (recipient != None) is hidden from
    the user, so it should still count as reasoning tokens."""
    context = HarmonyContext(messages=[], available_tools=[])

    mock_parser.current_channel = "commentary"
    mock_parser.current_recipient = "python"

    mock_output = create_mock_request_output(
        prompt_token_ids=[1, 2, 3],
        output_token_ids=[4, 5, 6],
        num_cached_tokens=0,
    )
    context.append_output(mock_output)

    assert context.num_reasoning_tokens == 3
    assert context.num_output_tokens == 3


def test_zero_tokens_edge_case():
    """Test behavior with all zero token counts."""
    context = HarmonyContext(messages=[], available_tools=[])

    # Create a request with empty lists (not None) for both prompt and
    # output tokens
    mock_output = create_mock_request_output(
        prompt_token_ids=[],  # Empty prompt tokens
        output_token_ids=[],  # Empty output tokens
        num_cached_tokens=0,
    )

    context.append_output(mock_output)

    # All counts should be zero
    assert context.num_prompt_tokens == 0
    assert context.num_output_tokens == 0
    assert context.num_cached_tokens == 0
    assert context.num_tool_output_tokens == 0
    assert context.num_reasoning_tokens == 0


@pytest.mark.asyncio
async def test_single_turn_no_tool_output():
    """Test that first turn never generates tool output tokens."""
    context = HarmonyContext(
        messages=[],
        available_tools=["browser"],  # Tools available
    )

    # Even with large prompt in first turn, no tool tokens should be counted
    mock_output = create_mock_request_output(
        prompt_token_ids=list(range(100)),  # 100 tokens
        output_token_ids=[1, 2, 3],
        num_cached_tokens=0,
    )

    context.append_output(mock_output)

    # First turn should never have tool output tokens
    assert context.num_tool_output_tokens == 0
    assert context.is_first_turn is False  # Should be updated after first turn


@pytest.mark.asyncio
async def test_negative_tool_tokens_edge_case():
    """Test edge case where calculation could result in negative tool
    tokens. We should log an error and clamp the value to 0."""
    # Use patch to check if logger.error was called
    with patch("vllm.entrypoints.openai.responses.context.logger.error") as mock_log:
        context = HarmonyContext(messages=[], available_tools=["browser"])

        # First turn
        mock_output1 = create_mock_request_output(
            prompt_token_ids=list(range(10)),  # 10 tokens
            output_token_ids=[1, 2, 3, 4, 5],  # 5 tokens
        )
        context.append_output(mock_output1)

        # Second turn with fewer new tokens than previous output
        # This could happen in edge cases with aggressive caching
        mock_output2 = create_mock_request_output(
            prompt_token_ids=list(range(12)),  # 12 tokens (only 2 new)
            output_token_ids=[6, 7],  # 2 tokens
        )
        context.append_output(mock_output2)

        # Calculated negative tool tokens (12 - 10 - 5 = -3) should be clamped
        # to 0 and an error should be logged
        assert context.num_tool_output_tokens == 0
        assert context.num_prompt_tokens == 10 + 12
        assert context.num_output_tokens == 5 + 2

        # Verify the error was logged properly
        mock_log.assert_called_once()

        # Extract the actual log message and arguments from the call
        args, _ = mock_log.call_args
        log_message = args[0]

        # Check for key parts of the message
        assert "Negative tool output tokens calculated" in log_message
        assert "-3" in str(args)  # Check that -3 is in the arguments


@pytest.mark.asyncio
async def test_streaming_multi_turn_token_counting(mock_parser):
    """Test token counting for streaming multi-turn conversations.

    This test focuses on how StreamingHarmonyContext counts tokens in a
    multi-turn conversation with streaming (token-by-token) outputs and
    message boundaries.
    """
    # Create a streaming context
    context = StreamingHarmonyContext(messages=[], available_tools=["browser"])

    num_prompt_tokens = [3, 8, 13]
    num_output_tokens = [3, 3, 2]
    num_cached_tokens = [0, 3, 8]

    # Simulate three turns of conversation:
    # Turn 1: stream tokens one by one, then finish the message
    # Turn 2: new prompt, stream more tokens with a reasoning segment
    # Turn 3: new prompt with tool output and cached tokens

    # First turn: 3 tokens streamed one by one
    # First token of first turn
    context.append_output(
        create_mock_request_output(
            prompt_token_ids=[1, 2, 3],  # 3 prompt tokens
            output_token_ids=[101],  # Single token
            num_cached_tokens=num_cached_tokens[0],
            finished=False,  # Not end of message yet
        )
    )

    # Second token of first turn
    context.append_output(
        create_mock_request_output(
            output_token_ids=[102],
            finished=False,
        )
    )

    # Last token of first turn (finished=True signals end of message)
    context.append_output(
        create_mock_request_output(
            output_token_ids=[103],
            finished=True,  # End of message
        )
    )

    # Check token counts after first turn
    assert context.num_prompt_tokens == 3  # Initial prompt tokens
    assert context.num_output_tokens == 3  # Three output tokens
    assert context.num_cached_tokens == 0
    assert context.num_tool_output_tokens == 0  # No tool output in first turn
    assert context.first_tok_of_message is True  # Ready for next message

    # Second turn: reasoning tokens in analysis channel
    mock_parser.current_channel = "analysis"  # Set to reasoning channel

    # First token of second turn
    context.append_output(
        create_mock_request_output(
            prompt_token_ids=[
                1,
                2,
                3,
                101,
                102,
                103,
                4,
                5,
            ],  # 8 tokens (includes previous)
            output_token_ids=[201],
            num_cached_tokens=num_cached_tokens[1],  # Some tokens cached
            finished=False,
        )
    )

    # More tokens in reasoning channel
    context.append_output(
        create_mock_request_output(
            output_token_ids=[202],
            finished=False,
        )
    )

    context.append_output(
        create_mock_request_output(
            output_token_ids=[203],
            finished=True,  # End of reasoning message
        )
    )

    # Check counts after second turn (reasoning message)
    assert context.num_prompt_tokens == 3 + 8  # Initial + second prompt
    assert context.num_output_tokens == 3 + 3  # First turn + second turn
    assert context.num_reasoning_tokens == 3  # All tokens in analysis channel
    assert context.num_cached_tokens == 3  # Cached tokens from second turn

    # Formula: this turn prompt tokens - last turn prompt - last turn output
    expected_tool_tokens = 8 - 3 - 3  # = 2
    assert context.num_tool_output_tokens == expected_tool_tokens

    # Third turn: regular output channel
    mock_parser.current_channel = "final"  # Switch back to regular channel

    # Third turn (with more cached tokens)
    context.append_output(
        create_mock_request_output(
            prompt_token_ids=[
                1,
                2,
                3,
                101,
                102,
                103,
                4,
                5,
                201,
                202,
                203,
                6,
                7,
            ],  # 13 tokens
            output_token_ids=[301],
            num_cached_tokens=num_cached_tokens[2],  # More cached tokens
            finished=False,
        )
    )

    context.append_output(
        create_mock_request_output(
            output_token_ids=[302],
            finished=True,
        )
    )

    # Final token counts check
    assert context.num_prompt_tokens == sum(num_prompt_tokens)  # All prompts
    assert context.num_output_tokens == sum(num_output_tokens)  # All outputs
    assert context.num_reasoning_tokens == 3  # Unchanged from second turn
    assert context.num_cached_tokens == sum(
        num_cached_tokens
    )  # Accumulated cached tokens

    # Additional tool tokens from third turn
    # Formula: this turn prompt - last turn prompt - last turn output
    additional_tool_tokens = 13 - 8 - 3  # = 2
    assert (
        context.num_tool_output_tokens == expected_tool_tokens + additional_tool_tokens
    )

    # Validate all turn metrics
    assert len(context.all_turn_metrics) == 3
    for i, turn in enumerate(context.all_turn_metrics):
        assert turn.input_tokens == num_prompt_tokens[i]
        assert turn.output_tokens == num_output_tokens[i]
        assert turn.cached_input_tokens == num_cached_tokens[i]
    assert context.all_turn_metrics[1].tool_output_tokens == 2
    assert context.all_turn_metrics[2].tool_output_tokens == 2


@pytest.mark.asyncio
async def test_streaming_message_synchronization(mock_parser):
    """Test message synchronization logic from lines 413-417 in context.py.

    This test verifies that when parser.messages contains more messages than
    the context's _messages (minus initial messages), the context properly
    extends its message list with the new parser messages.
    """

    # Create a streaming context with some initial messages
    initial_messages = [
        Message(
            author=Author(role=Role.USER, name="user"),
            content=[TextContent(text="Hello")],
            recipient=Role.ASSISTANT,
        )
    ]
    context = StreamingHarmonyContext(messages=initial_messages, available_tools=[])

    # Verify initial state
    assert len(context._messages) == 1
    assert context.num_init_messages == 1

    # Mock parser to have more messages than context
    # Simulate parser having processed 3 new messages
    mock_parser.messages = [
        Message(
            author=Author(role=Role.ASSISTANT, name="assistant"),
            content=[TextContent(text="Response 1")],
            recipient=Role.USER,
        ),
    ]

    # This should trigger the message synchronization logic
    context.append_output(
        create_mock_request_output(
            prompt_token_ids=[1, 2, 3], output_token_ids=[101], finished=False
        )
    )

    # Verify that messages were synchronized
    assert len(context._messages) == 2

    # Verify the new messages were added correctly
    assert context._messages[1].content[0].text == "Response 1"

    # Test the specific condition from line 413-414:
    # len(self._messages) - self.num_init_messages < len(self.parser.messages)
    messages_minus_init = len(context._messages) - context.num_init_messages
    parser_messages_count = len(mock_parser.messages)

    # After synchronization, they should be equal (no longer less than)
    assert messages_minus_init == parser_messages_count

    # Test edge case: add one more parser message
    mock_parser.messages.append(
        Message(
            author=Author(role=Role.ASSISTANT, name="assistant"),
            content=[TextContent(text="Response 4")],
            recipient=Role.USER,
        )
    )

    # Create another output to trigger synchronization again
    mock_output2 = create_mock_request_output(
        prompt_token_ids=[1, 2, 3], output_token_ids=[102], finished=True
    )

    context.append_output(mock_output2)

    # Verify the fourth message was added, num_init_messages is still 1
    assert len(context._messages) == 3
    assert context.num_init_messages == 1
    assert context._messages[2].content[0].text == "Response 4"


def test_turn_metrics_copy_and_reset():
    """Test TurnMetrics copy and reset methods work correctly."""
    # Create a TurnMetrics with specific values
    original_metrics = TurnMetrics(
        input_tokens=10,
        output_tokens=20,
        cached_input_tokens=5,
        tool_output_tokens=3,
    )

    # Test copy functionality
    copied_metrics = original_metrics.copy()

    # Verify copy has same values
    assert copied_metrics.input_tokens == 10
    assert copied_metrics.output_tokens == 20
    assert copied_metrics.cached_input_tokens == 5
    assert copied_metrics.tool_output_tokens == 3

    # Verify they are separate objects
    assert copied_metrics is not original_metrics

    # Modify copy to ensure independence
    copied_metrics.input_tokens = 999
    assert original_metrics.input_tokens == 10  # Original unchanged
    assert copied_metrics.input_tokens == 999

    # Test reset functionality
    original_metrics.reset()

    # Verify all fields are reset to zero
    assert original_metrics.input_tokens == 0
    assert original_metrics.output_tokens == 0
    assert original_metrics.cached_input_tokens == 0
    assert original_metrics.tool_output_tokens == 0

    # Verify copied metrics are unaffected by reset
    assert copied_metrics.input_tokens == 999
    assert copied_metrics.output_tokens == 20
    assert copied_metrics.cached_input_tokens == 5
    assert copied_metrics.tool_output_tokens == 3


# ==================== SimpleContext Tests ====================


def create_simple_context_output(
    text="",
    token_ids=None,
    prompt="Test prompt",
    prompt_token_ids=None,
    num_cached_tokens=0,
    logprobs=None,
    finished=True,
):
    """Helper to create a RequestOutput with customizable text for
    SimpleContext tests."""
    if token_ids is None:
        token_ids = []
    return RequestOutput(
        request_id="test-id",
        prompt=prompt,
        prompt_token_ids=prompt_token_ids,
        prompt_logprobs=None,
        outputs=[
            CompletionOutput(
                index=0,
                text=text,
                token_ids=token_ids,
                cumulative_logprob=0.0,
                logprobs=logprobs,
                finish_reason=None,
                stop_reason=None,
            )
        ],
        finished=finished,
        num_cached_tokens=num_cached_tokens,
    )


def test_simple_context_output_messages_empty():
    """output_messages should be empty before any output is appended."""
    context = SimpleContext()
    assert context.output_messages == []


def test_simple_context_output_messages_single_call():
    """Non-streaming: single append_output produces a single output message."""
    context = SimpleContext()
    output = create_simple_context_output(
        text="Hello world",
        token_ids=[10, 20, 30],
        prompt_token_ids=[1, 2, 3],
    )
    context.append_output(output)

    messages = context.output_messages
    assert len(messages) == 1
    assert messages[0].message == "Hello world"
    assert messages[0].tokens == [10, 20, 30]
    assert messages[0].type == "raw_message_tokens"


def test_simple_context_output_messages_streaming_consolidation():
    """Streaming: multiple append_output calls consolidate into one message."""
    context = SimpleContext()

    # Simulate 3 streaming deltas
    context.append_output(
        create_simple_context_output(
            text="Hello",
            token_ids=[10],
            prompt_token_ids=[1, 2, 3],
        )
    )
    context.append_output(
        create_simple_context_output(
            text=" world",
            token_ids=[20],
            prompt_token_ids=[1, 2, 3],
        )
    )
    context.append_output(
        create_simple_context_output(
            text="!",
            token_ids=[30],
            prompt_token_ids=[1, 2, 3],
        )
    )

    messages = context.output_messages
    assert len(messages) == 1
    assert messages[0].message == "Hello world!"
    assert messages[0].tokens == [10, 20, 30]


def test_simple_context_output_messages_many_deltas():
    """Streaming with many small deltas still produces a single message."""
    context = SimpleContext()

    words = ["The", " quick", " brown", " fox", " jumps"]
    for i, word in enumerate(words):
        context.append_output(
            create_simple_context_output(
                text=word,
                token_ids=[100 + i],
                prompt_token_ids=[1, 2],
            )
        )

    messages = context.output_messages
    assert len(messages) == 1
    assert messages[0].message == "The quick brown fox jumps"
    assert messages[0].tokens == [100, 101, 102, 103, 104]


def test_simple_context_input_messages():
    """input_messages is populated on the first append_output call."""
    context = SimpleContext()
    assert context.input_messages == []

    context.append_output(
        create_simple_context_output(
            text="Hi",
            token_ids=[10],
            prompt="My prompt text",
            prompt_token_ids=[1, 2, 3],
        )
    )

    assert len(context.input_messages) == 1
    assert context.input_messages[0].message == "My prompt text"
    assert context.input_messages[0].tokens == [1, 2, 3]

    # Second call should not add another input message
    context.append_output(
        create_simple_context_output(
            text=" there",
            token_ids=[20],
            prompt="My prompt text",
            prompt_token_ids=[1, 2, 3],
        )
    )

    assert len(context.input_messages) == 1


def test_simple_context_token_counting():
    """Token counting accumulates across streaming deltas."""
    context = SimpleContext()

    context.append_output(
        create_simple_context_output(
            text="a",
            token_ids=[10, 11],
            prompt_token_ids=[1, 2, 3, 4, 5],
            num_cached_tokens=2,
        )
    )
    context.append_output(
        create_simple_context_output(
            text="b",
            token_ids=[12],
            prompt_token_ids=[1, 2, 3, 4, 5],
            num_cached_tokens=2,
        )
    )

    assert context.num_prompt_tokens == 5
    assert context.num_output_tokens == 3  # 2 + 1
    assert context.num_cached_tokens == 2


def test_simple_context_final_output():
    """final_output reconstructs accumulated text and token_ids."""
    context = SimpleContext()

    context.append_output(
        create_simple_context_output(
            text="foo",
            token_ids=[1, 2],
            prompt_token_ids=[10],
        )
    )
    context.append_output(
        create_simple_context_output(
            text="bar",
            token_ids=[3],
            prompt_token_ids=[10],
        )
    )

    final = context.final_output
    assert final is not None
    assert final.outputs[0].text == "foobar"
    assert final.outputs[0].token_ids == (1, 2, 3)


def test_simple_context_output_messages_empty_text_with_tokens():
    """output_messages should be returned when tokens exist even if text is
    empty (e.g. special tokens)."""
    context = SimpleContext()
    context.append_output(
        create_simple_context_output(
            text="",
            token_ids=[99],
            prompt_token_ids=[1],
        )
    )

    messages = context.output_messages
    assert len(messages) == 1
    assert messages[0].message == ""
    assert messages[0].tokens == [99]


def test_simple_context_output_messages_no_mutation():
    """Each call to output_messages returns a fresh list; callers can't
    corrupt internal state."""
    context = SimpleContext()
    context.append_output(
        create_simple_context_output(
            text="hello",
            token_ids=[1],
            prompt_token_ids=[10],
        )
    )

    msgs1 = context.output_messages
    msgs2 = context.output_messages
    assert msgs1 is not msgs2
    assert msgs1[0].message == msgs2[0].message

    # Appending more output updates the property
    context.append_output(
        create_simple_context_output(
            text=" world",
            token_ids=[2],
            prompt_token_ids=[10],
        )
    )

    msgs3 = context.output_messages
    assert len(msgs3) == 1
    assert msgs3[0].message == "hello world"
    assert msgs3[0].tokens == [1, 2]