How to use the ghstack.shell.Shell function in ghstack

def setUp(self) -> None:
        # Set up a "parent" repository with an empty initial commit that we'll operate on
        upstream_dir = tempfile.mkdtemp()
        if GH_KEEP_TMP:
            self.addCleanup(lambda: print("upstream_dir preserved at: {}".format(upstream_dir)))
        else:
            self.addCleanup(lambda: shutil.rmtree(upstream_dir))
        self.upstream_sh = ghstack.shell.Shell(cwd=upstream_dir, testing=True)
        # I plan to fix this type error soon
        self.github = ghstack.github_fake.FakeGitHubEndpoint(self.upstream_sh)

        local_dir = tempfile.mkdtemp()
        if GH_KEEP_TMP:
            self.addCleanup(lambda: print("local_dir preserved at: {}".format(local_dir)))
        else:
            self.addCleanup(lambda: shutil.rmtree(local_dir))
        self.sh = ghstack.shell.Shell(cwd=local_dir, testing=True)
        self.sh.git("clone", upstream_dir, ".")

        self.rev_map = {}
        self.substituteRev(GitCommitHash("HEAD"), SubstituteRev("rINI0"))

def strip_trailing_whitespace(text: str) -> str:
    return re.sub(r' +$', '', text, flags=re.MULTILINE)


def indent(text: str, prefix: str) -> str:
    return ''.join(prefix + line if line.strip() else line
                   for line in text.splitlines(True))


class TestGh(expecttest.TestCase):
    proc: ClassVar[subprocess.Popen]
    github: ghstack.github.GitHubEndpoint
    rev_map: Dict[SubstituteRev, GitCommitHash]
    upstream_sh: ghstack.shell.Shell
    sh: ghstack.shell.Shell

    def setUp(self) -> None:
        # Set up a "parent" repository with an empty initial commit that we'll operate on
        upstream_dir = tempfile.mkdtemp()
        if GH_KEEP_TMP:
            self.addCleanup(lambda: print("upstream_dir preserved at: {}".format(upstream_dir)))
        else:
            self.addCleanup(lambda: shutil.rmtree(upstream_dir))
        self.upstream_sh = ghstack.shell.Shell(cwd=upstream_dir, testing=True)
        # I plan to fix this type error soon
        self.github = ghstack.github_fake.FakeGitHubEndpoint(self.upstream_sh)

        local_dir = tempfile.mkdtemp()
        if GH_KEEP_TMP:
            self.addCleanup(lambda: print("local_dir preserved at: {}".format(local_dir)))
        else: