test: add integration tests for dynamic tooling

Author: Kyon Caldera

tests/integ/mcp/simple_mcp_server/mcp_server.py

@@ -20,6 +20,28 @@ def greet(name: str):
     return f'Hello {name}'
 
 
+##### Dynamic Tool Testing
+
+_multiply_registered = False
+
+
+@mcp.tool
+def add_tool_multiply():
+    """MCP Tool used for testing dynamic tool behavior through the proxy."""
+    global _multiply_registered
+
+    if not _multiply_registered:
+
+        @mcp.tool
+        def multiply(x: int, y: int):
+            """Multiply two numbers."""
+            return x * y
+
+        _multiply_registered = True
+        return 'Tool "multiply" added successfully'
+    return 'Tool "multiply" already exists'
+
+
 ##### Elicitation Testing
 
 

tests/integ/test_proxy_dynamic_tools.py

@@ -0,0 +1,47 @@
+"""Integration tests for dynamic tool behavior through the proxy."""
+
+import fastmcp
+import logging
+import pytest
+
+
+logger = logging.getLogger(__name__)
+
+
+@pytest.mark.asyncio(loop_scope='module')
+async def test_proxy_reflects_tool_addition(mcp_client: fastmcp.Client):
+    """Test that when backend dynamically adds a tool, proxy reflects it on next list_tools call."""
+    # Arrange - Get initial tool list
+    initial_tools = await mcp_client.list_tools()
+    initial_tool_names = [tool.name for tool in initial_tools]
+
+    logger.info(f'Initial tools: {initial_tool_names}')
+
+    # Verify 'multiply' tool doesn't exist yet
+    assert 'multiply' not in initial_tool_names, 'multiply tool should not exist initially'
+
+    # Act - Trigger backend to dynamically add a new tool
+    logger.info('Calling add_tool_multiply to add a new tool to the backend')
+    add_result = await mcp_client.call_tool('add_tool_multiply', {})
+    logger.info(f'Backend response: {add_result}')
+
+    # Get updated tool list
+    updated_tools = await mcp_client.list_tools()
+    updated_tool_names = [tool.name for tool in updated_tools]
+
+    logger.info(f'Updated tools: {updated_tool_names}')
+
+    # Assert
+    # The proxy should reflect the newly added tool
+    assert 'multiply' in updated_tool_names, 'multiply tool should now exist after adding'
+    assert len(updated_tools) == len(initial_tools) + 1, 'Should have one more tool'
+
+    # Verify the new tool actually works
+    logger.info('Testing the newly added multiply tool')
+    multiply_result = await mcp_client.call_tool('multiply', {'x': 6, 'y': 7})
+
+    # Extract the result (handling different response formats)
+    from tests.integ.test_proxy_simple_mcp_server import get_text_content
+
+    result_text = get_text_content(multiply_result)
+    assert result_text == '42', f'multiply(6, 7) should return 42, got {result_text}'