How to use testclient with selenium in pytest?

[sneakers-the-rat]

Hello!! I have done a decent bit of searching around and can't quite find an answer already, hopefully this is not too obvious to those more familiar with the package.

I am trying to test a fastapi app (that uses the starlette TestClient, which is ultimately an httpx client) using selenium, and can't quite figure out how to forward the webdriver tests to the transport handlers running the WSGI application. Any advice would be very much appreciated :)

[BenkiNew]

TestClient (and httpx's ASGITransport/WSGITransport) call your app in-process; its base URL http://testserver doesn't exist on the network. A Selenium-driven browser is a separate process that only speaks real TCP/HTTP, so its requests can't be routed through that transport. The usual approach is a "live server" fixture: run the app on a real port in a background thread and point the driver at it.

ASGI (FastAPI/Starlette):

import socket, threading, time
import pytest, uvicorn

@pytest.fixture(scope="session")
def live_server():
    with socket.socket() as s:                    # free port from the OS
        s.bind(("127.0.0.1", 0))
        port = s.getsockname()[1]
    server = uvicorn.Server(uvicorn.Config(app, host="127.0.0.1", port=port, log_level="error"))
    thread = threading.Thread(target=server.run, daemon=True)
    thread.start()
    deadline = time.monotonic() + 10
    while not server.started:                     # wait until it is really listening
        if not thread.is_alive() or time.monotonic() > deadline:
            raise RuntimeError("test server failed to start")
        time.sleep(0.01)
    yield f"http://127.0.0.1:{port}"
    server.should_exit = True
    thread.join(timeout=5)

WSGI (e.g. Flask): srv = wsgiref.simple_server.make_server("127.0.0.1", 0, app) run with srv.serve_forever in a thread (srv.server_port gives the port, srv.shutdown() on teardown), or werkzeug's make_server.

Then use driver.get(f"{live_server}/...") in the test. If you only need to test the API rather than the browser UI, keep using TestClient — no server needed.

[ketpatil77]

The live-server approach in the earlier reply is correct. One fixture detail is worth changing: keep the OS-assigned socket open and pass that socket to Uvicorn. Closing it after finding the port leaves a race before the server binds it, especially in parallel test runs.

import socket
import threading
import time
import pytest
import uvicorn

@pytest.fixture(scope='session')
def live_server():
    # Import your FastAPI app here.
    from myapp import app

    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as sock:
        sock.bind(('127.0.0.1', 0))
        port = sock.getsockname()[1]
        server = uvicorn.Server(uvicorn.Config(app, log_level='error'))
        thread = threading.Thread(
            target=server.run, kwargs={'sockets': [sock]}, daemon=True
        )
        thread.start()
        try:
            deadline = time.monotonic() + 10
            while not server.started:
                if not thread.is_alive() or time.monotonic() >= deadline:
                    raise RuntimeError('Test server did not start')
                time.sleep(0.01)
            yield f'http://127.0.0.1:{port}'
        finally:
            server.should_exit = True
            thread.join(timeout=5)

Then use driver.get(live_server + '/your-page'). Adjust myapp to your module. I checked a real loopback HTTP request and clean server shutdown with Uvicorn 0.54.0 / FastAPI 0.162.0; I did not run Selenium.

This address is suitable for a browser on the same machine/network namespace. A remote Selenium container needs an address reachable from that container. Also, TestClient dependency overrides, cookies, and transactions do not automatically transfer to an independently started app process.

Uvicorn's supplied-socket handling.