add test for chat context (#2677)

# Add Comprehensive Tests for Chat Context Module

## Overview
This PR adds comprehensive test coverage for the `chat_context` module,
ensuring robust testing of message history management, session
isolation, and OpenAI format conversion functionality.

## Changes
- **New Test File**: `backend/tests/test_chat_context.py` with 28 test
cases
- **Test Coverage**: Message management (get, add, remove, clear),
OpenAI conversion, and edge cases
- **Context Helper**: Custom `mock_chainlit_context()` helper for proper
Chainlit context initialization

## Test Suites

### 1. Core Functionality Tests (22 tests)
- **`get()` method** (4 tests)
  - Returns empty list without session
  - Creates new chat context for new sessions
  - Returns copy of messages (not original reference)
  - Retrieves existing messages correctly

- **`add()` method** (5 tests)
  - Does nothing without session
  - Creates new context and adds message
  - Appends to existing context
  - Prevents duplicate messages
  - Returns message for method chaining

- **`remove()` method** (5 tests)
  - Returns False without session
  - Returns False for nonexistent context
  - Returns False for nonexistent message
  - Successfully removes existing message
  - Maintains remaining messages after removal

- **`clear()` method** (3 tests)
  - Does nothing without session
  - Does nothing for nonexistent context
  - Empties existing context while preserving structure

- **`to_openai()` method** (10 tests)
- Converts assistant messages to `{"role": "assistant", "content":
"..."}`
  - Converts user messages to `{"role": "user", "content": "..."}`
  - Converts system messages to `{"role": "system", "content": "..."}`
  - Treats unknown message types as system messages
  - Handles multiple messages in sequence
  - Returns empty list for empty context
  - Returns empty list without session

### 2. Edge Cases Tests (6 tests)
- **Session Isolation**: Different sessions maintain separate message
contexts
- **Operation Sequences**: Add → Remove → Add again workflow
- **Clear and Add**: Adding messages after clearing context
- **Mixed Message Types**: Various message types in OpenAI conversion
- **Singleton Verification**: `chat_context` instance consistency
- **Return Value Chaining**: `add()` returns message for fluent API

## Technical Implementation

### Context Helper Function
```python
@contextmanager
def mock_chainlit_context(session=None):
    """Context manager to set up and tear down Chainlit context."""
    # Mock the event loop since we're not in an async context
    mock_loop = Mock(spec=asyncio.AbstractEventLoop)
    
    with patch("asyncio.get_running_loop", return_value=mock_loop):
        mock_context = ChainlitContext(session=session)
        token = context_var.set(mock_context)
        try:
            yield mock_context
        finally:
            context_var.reset(token)
```

### Key Features
- **Event Loop Mocking**: Patches `asyncio.get_running_loop()` to avoid
"no running event loop" errors in synchronous tests
- **Context Variable Management**: Properly sets and resets
`context_var` using tokens
- **Session Mocking**: Creates mock sessions with configurable IDs for
testing
- **Proper Cleanup**: `setup_method()` and `teardown_method()` clear
`chat_contexts` dictionary

## Coverage Details
- **Total Tests**: 28
- **Synchronous Tests**: All tests are synchronous (no async/await)
- **Mocking Strategy**: Uses `Mock` for sessions and messages, `patch`
for event loop
- **Cross-Platform**: Compatible with Windows and Linux environments

## Testing Approach
- **Context Initialization**: Uses custom helper to properly initialize
Chainlit context
- **Message Mocking**: Creates mock message objects with `type` and
`content` attributes
- **Session Isolation**: Tests verify that different sessions don't
interfere with each other
- **State Management**: Proper setup/teardown ensures test isolation

## Related Modules
- `chainlit.chat_context`: Message history management
- `chainlit.context`: Chainlit context and context variables
- `chainlit.message`: Message types and structures

Contribution by Gittensor, learn more at https://gittensor.io/

---------

Co-authored-by: Josh Hayes <35790761+hayescode@users.noreply.github.com>

Author: codomposer