def test_client_certs_one_file(self) -> None:
        """
        Having a client cert and its associated private key in just one file
        works properly.
        """
        done_receiving = Event()
        client_certs = []

        def socket_handler(listener: socket.socket) -> None:
            sock = listener.accept()[0]
            sock = self._wrap_in_ssl(sock)

            client_certs.append(sock.getpeercert())

            data = b""
            while not data.endswith(b"\r\n\r\n"):
                data += sock.recv(8192)

            sock.sendall(
                b"HTTP/1.1 200 OK\r\n"
                b"Server: testsocket\r\n"
                b"Connection: close\r\n"
                b"Content-Length: 6\r\n"
                b"\r\n"
                b"Valid!"
            )

            done_receiving.wait(5)
            sock.close()

        self._start_server(socket_handler)
        with HTTPSConnectionPool(
            self.host,
            self.port,
            cert_file=self.cert_combined_path,
            cert_reqs="REQUIRED",
            ca_certs=self.ca_path,
        ) as pool:
            pool.request("GET", "/", retries=0)
            done_receiving.set()

            assert len(client_certs) == 1

        Having a client cert and its associated private key in just one file
        works properly.
        
test/with_dummyserver/test_socketlevel.py