test_auth.py

            Performs one refresh, returning the next refresh token and access token.
            """
            refresh_response = self.use_refresh_token(refresh_token)
            self.assertEqual(
                refresh_response.code, HTTPStatus.OK, refresh_response.result
            )
            return (
                refresh_response.json_body["refresh_token"],
                refresh_response.json_body["access_token"],
            )

        def _table_length(table_name: str) -> int:
            """
            Helper to get the size of a table, in rows.
            For testing only; trivially vulnerable to SQL injection.
            """

            def _txn(txn: LoggingTransaction) -> int:
                txn.execute(f"SELECT COUNT(1) FROM {table_name}")
                row = txn.fetchone()
                # Query is infallible
                assert row is not None
                return row[0]

            return self.get_success(
                self.hs.get_datastores().main.db_pool.runInteraction(
                    "_table_length", _txn
                )
            )

        # Before we log in, there are no access tokens.
        self.assertEqual(_table_length("access_tokens"), 0)
        self.assertEqual(_table_length("refresh_tokens"), 0)

        body = {
            "type": "m.login.password",
            "user": "test",
            "password": self.user_pass,
            "refresh_token": True,
        }
        login_response = self.make_request(
            "POST",
            "/_matrix/client/v3/login",
            body,
        )
        self.assertEqual(login_response.code, HTTPStatus.OK, login_response.result)

        access_token = login_response.json_body["access_token"]
        refresh_token = login_response.json_body["refresh_token"]

        # Now that we have logged in, there should be one access token and one
        # refresh token
        self.assertEqual(_table_length("access_tokens"), 1)
        self.assertEqual(_table_length("refresh_tokens"), 1)

        for _ in range(5):
            refresh_token, access_token = _refresh(refresh_token)

        # After 5 sequential refreshes, there should only be the latest two
        # refresh/access token pairs.
        # (The last one is preserved because it's in use!
        # The one before that is preserved because it can still be used to
        # replace the last token pair, in case of e.g. a network interruption.)
        self.assertEqual(_table_length("access_tokens"), 2)
        self.assertEqual(_table_length("refresh_tokens"), 2)

        logout_response = self.make_request(
            "POST", "/_matrix/client/v3/logout", {}, access_token=access_token
        )
        self.assertEqual(logout_response.code, HTTPStatus.OK, logout_response.result)

        # Now that we have logged in, there should be no access token
        # and no refresh token
        self.assertEqual(_table_length("access_tokens"), 0)
        self.assertEqual(_table_length("refresh_tokens"), 0)