Replace subprocess tests with in-process async servers (#2006)

* Use anyio as testing backend

* Remove asyncio markers

* Update streamable http tests

* Replace all subprocess tests

* Replace anyio task groups with asyncio context managers in tests

- Convert run_server_async from anyio task group pattern to asyncio.create_task with async context manager
- Remove task_group fixture from conftest
- Update all test fixtures to use async with run_server_async pattern
- Remove TaskGroup imports from all test files
- Tests now work with pytest-asyncio instead of pytest-anyio

* Update test_github_provider_integration.py

tests/integration_tests/auth/test_github_provider_integration.py

@@ -12,7 +12,7 @@ with the following configuration:
 
 import os
 import re
-from collections.abc import Generator
+from collections.abc import AsyncGenerator
 from urllib.parse import parse_qs, urlparse
 
 import httpx
@@ -21,7 +21,7 @@ import pytest
 from fastmcp import FastMCP
 from fastmcp.client import Client
 from fastmcp.server.auth.providers.github import GitHubProvider
-from fastmcp.utilities.tests import HeadlessOAuth, run_server_in_process
+from fastmcp.utilities.tests import HeadlessOAuth, run_server_async
 
 FASTMCP_TEST_AUTH_GITHUB_CLIENT_ID = os.getenv("FASTMCP_TEST_AUTH_GITHUB_CLIENT_ID")
 FASTMCP_TEST_AUTH_GITHUB_CLIENT_SECRET = os.getenv(
@@ -36,7 +36,7 @@ pytestmark = pytest.mark.xfail(
 )
 
 
-def create_github_server(host: str = "127.0.0.1", port: int = 9100, **kwargs) -> None:
+def create_github_server(base_url: str) -> FastMCP:
     """Create FastMCP server with GitHub OAuth protection."""
     assert FASTMCP_TEST_AUTH_GITHUB_CLIENT_ID is not None
     assert FASTMCP_TEST_AUTH_GITHUB_CLIENT_SECRET is not None
@@ -45,7 +45,7 @@ def create_github_server(host: str = "127.0.0.1", port: int = 9100, **kwargs) ->
     auth = GitHubProvider(
         client_id=FASTMCP_TEST_AUTH_GITHUB_CLIENT_ID,
         client_secret=FASTMCP_TEST_AUTH_GITHUB_CLIENT_SECRET,
-        base_url=f"http://{host}:{port}",
+        base_url=base_url,
     )
 
     # Create FastMCP server with GitHub authentication
@@ -61,13 +61,10 @@ def create_github_server(host: str = "127.0.0.1", port: int = 9100, **kwargs) ->
         """Returns user info from OAuth context."""
         return "📝 GitHub OAuth user authenticated successfully"
 
-    # Run the server
-    server.run(host=host, port=port, **kwargs)
+    return server
 
 
-def create_github_server_with_mock_callback(
-    host: str = "127.0.0.1", port: int = 9100, **kwargs
-) -> None:
+def create_github_server_with_mock_callback(base_url: str) -> FastMCP:
     """Create FastMCP server with GitHub OAuth that mocks the callback for testing."""
     assert FASTMCP_TEST_AUTH_GITHUB_CLIENT_ID is not None
     assert FASTMCP_TEST_AUTH_GITHUB_CLIENT_SECRET is not None
@@ -76,7 +73,7 @@ def create_github_server_with_mock_callback(
     auth = GitHubProvider(
         client_id=FASTMCP_TEST_AUTH_GITHUB_CLIENT_ID,
         client_secret=FASTMCP_TEST_AUTH_GITHUB_CLIENT_SECRET,
-        base_url=f"http://{host}:{port}",
+        base_url=base_url,
     )
 
     # Mock the authorize method to return a fake code instead of redirecting to GitHub
@@ -159,29 +156,31 @@ def create_github_server_with_mock_callback(
         """Returns user info from OAuth context."""
         return "📝 GitHub OAuth user authenticated successfully"
 
-    # Run the server
-    server.run(host=host, port=port, **kwargs)
+    return server
 
 
-@pytest.fixture(scope="module")
-def github_server() -> Generator[str, None, None]:
-    """Start GitHub OAuth server in background process on fixed port 9100."""
-    with run_server_in_process(
-        create_github_server, transport="http", host="127.0.0.1", port=9100
-    ) as url:
-        yield f"{url}/mcp"
+@pytest.fixture
+async def github_server() -> AsyncGenerator[str, None]:
+    """Start GitHub OAuth server on a random available port."""
+    from fastmcp.utilities.http import find_available_port
+
+    port = find_available_port()
+    base_url = f"http://127.0.0.1:{port}"
+    server = create_github_server(base_url)
+    async with run_server_async(server, port=port, transport="http") as url:
+        yield url
 
 
-@pytest.fixture(scope="module")
-def github_server_with_mock() -> Generator[str, None, None]:
-    """Start GitHub OAuth server with mocked callback in background process on port 9101."""
-    with run_server_in_process(
-        create_github_server_with_mock_callback,
-        transport="http",
-        host="127.0.0.1",
-        port=9101,
-    ) as url:
-        yield f"{url}/mcp"
+@pytest.fixture
+async def github_server_with_mock() -> AsyncGenerator[str, None]:
+    """Start GitHub OAuth server with mocked callback on a random available port."""
+    from fastmcp.utilities.http import find_available_port
+
+    port = find_available_port()
+    base_url = f"http://127.0.0.1:{port}"
+    server = create_github_server_with_mock_callback(base_url)
+    async with run_server_async(server, port=port, transport="http") as url:
+        yield url
 
 
 @pytest.fixture