def METHOD_NAME(self):
    with self.assertRaisesRegex(KeyError, "real/shadow_me was already set"):
        self._nspawn_in(
            _SRC_SUBVOL_PAIR,
            [
                *(
                    "--shadow-path",
                    "/real/shadow_me",
                    "/real_i_will_shadow",
                ),
                *("--shadow-path", "/real/shadow_me", "/other_file"),
                "--",
                "bad_command_never_runs",
            ],
        )