How to use the dvc.system.System.is_symlink function in dvc

def test(self):
        ret = main(["config", "cache.type", "symlink"])
        self.assertEqual(ret, 0)

        ret = main(["add", self.FOO])
        self.assertEqual(ret, 0)

        shutil.rmtree(self.dvc.cache.local.cache_dir)

        self.assertTrue(System.is_symlink(self.FOO))

        ret = main(["remove", self.FOO + ".dvc"])
        self.assertEqual(ret, 0)

        self.assertFalse(os.path.lexists(self.FOO))

def test_readding_dir_should_not_unprotect_all(tmp_dir, dvc, mocker):
    tmp_dir.gen("dir/data", "data")

    dvc.cache.local.cache_types = ["symlink"]
    dvc.cache.local.protected = True

    dvc.add("dir")
    tmp_dir.gen("dir/new_file", "new_file_content")

    unprotect_spy = spy(RemoteLOCAL.unprotect)
    mocker.patch.object(RemoteLOCAL, "unprotect", unprotect_spy)
    dvc.add("dir")

    assert not unprotect_spy.mock.called
    assert System.is_symlink(os.path.join("dir", "new_file"))

foo_stage, = dvc_repo.add(repo_dir.FOO)
    data_dir_stage, = dvc_repo.add(repo_dir.DATA_DIR)

    dvc_repo.destroy()

    assert not os.path.exists(dvc_repo.dvc_dir)
    assert not os.path.exists(foo_stage.path)
    assert not os.path.exists(data_dir_stage.path)

    assert os.path.isfile(repo_dir.FOO)
    assert os.path.isdir(repo_dir.DATA_DIR)
    assert os.path.isfile(repo_dir.DATA)
    assert os.path.isdir(repo_dir.DATA_SUB_DIR)
    assert os.path.isfile(repo_dir.DATA_SUB)

    assert not System.is_symlink(repo_dir.FOO)
    assert not System.is_symlink(repo_dir.DATA_DIR)
    assert not System.is_symlink(repo_dir.DATA)
    assert not System.is_symlink(repo_dir.DATA_SUB)

dvc_repo.destroy()

    assert not os.path.exists(dvc_repo.dvc_dir)
    assert not os.path.exists(foo_stage.path)
    assert not os.path.exists(data_dir_stage.path)

    assert os.path.isfile(repo_dir.FOO)
    assert os.path.isdir(repo_dir.DATA_DIR)
    assert os.path.isfile(repo_dir.DATA)
    assert os.path.isdir(repo_dir.DATA_SUB_DIR)
    assert os.path.isfile(repo_dir.DATA_SUB)

    assert not System.is_symlink(repo_dir.FOO)
    assert not System.is_symlink(repo_dir.DATA_DIR)
    assert not System.is_symlink(repo_dir.DATA)
    assert not System.is_symlink(repo_dir.DATA_SUB)

        ("symlink", "copy", lambda path: not System.is_symlink(path)),
        ("copy", "hardlink", System.is_hardlink),

def _unprotect_file(self, path):
        import stat
        import uuid
        from dvc.system import System
        from dvc.utils import copyfile, move, remove

        if System.is_symlink(path) or System.is_hardlink(path):
            logger.debug("Unprotecting '{}'".format(path))

            tmp = os.path.join(os.path.dirname(path), "." + str(uuid.uuid4()))
            move(path, tmp)

            copyfile(tmp, path)

            remove(tmp)
        else:
            logger.debug(
                "Skipping copying for '{}', since it is not "
                "a symlink or a hardlink.".format(path)
            )

        os.chmod(path, os.stat(path).st_mode | stat.S_IWRITE)

def contains_symlink_up_to(path, base_path):
    base_path = fspath(base_path)
    path = fspath(path)

    if base_path not in path:
        raise BasePathNotInCheckedPathException(path, base_path)

    if path == base_path:
        return False
    if System.is_symlink(path):
        return True
    if os.path.dirname(path) == path:
        return False
    return contains_symlink_up_to(os.path.dirname(path), base_path)

def _unprotect_file(path):
    if System.is_symlink(path) or System.is_hardlink(path):
        logger.debug("Unprotecting '{}'".format(path))

        tmp = os.path.join(os.path.dirname(path), "." + str(uuid.uuid4()))
        move(path, tmp)

        copyfile(tmp, path)

        remove(tmp)
    else:
        logger.debug(
            "Skipping copying for '{}', since it is not "
            "a symlink or a hardlink.".format(path)
        )

    os.chmod(path, os.stat(path).st_mode | stat.S_IWRITE)