How to use the testpath.assert_isdir function in testpath

def test_wheel_src_module(copy_sample):
    td = copy_sample('module3')
    make_wheel_in(td / 'flit.ini', td)

    whl_file = td / 'module3-0.1-py2.py3-none-any.whl'
    assert_isfile(whl_file)
    with unpack(whl_file) as unpacked:
        assert_isfile(Path(unpacked, 'module3.py'))
        assert_isdir(Path(unpacked, 'module3-0.1.dist-info'))
        assert_isfile(Path(unpacked, 'module3-0.1.dist-info', 'LICENSE'))

def test_dist_name(self):
        Installer.from_ini_path(samples_dir / 'altdistname' / 'pyproject.toml').install_directly()
        assert_isdir(self.tmpdir / 'site-packages' / 'package1')
        assert_isdir(self.tmpdir / 'site-packages' / 'package_dist1-0.1.dist-info')

def test_dist_name(copy_sample):
    td = copy_sample('altdistname')
    make_wheel_in(td / 'flit.ini', td)
    res = td / 'package_dist1-0.1-py2.py3-none-any.whl'
    assert_isfile(res)
    with unpack(res) as td_unpack:
        assert_isdir(Path(td_unpack, 'package_dist1-0.1.dist-info'))

def test_install_package(self):
        oldcwd = os.getcwd()
        os.chdir(str(samples_dir / 'package1'))
        try:
            Installer.from_ini_path(pathlib.Path('pyproject.toml')).install_directly()
        finally:
            os.chdir(oldcwd)
        assert_isdir(self.tmpdir / 'site-packages' / 'package1')
        assert_isdir(self.tmpdir / 'site-packages' / 'package1-0.1.dist-info')
        assert_isfile(self.tmpdir / 'scripts' / 'pkg_script')
        with (self.tmpdir / 'scripts' / 'pkg_script').open() as f:
            assert f.readline().strip() == "#!" + sys.executable
        self._assert_direct_url(
            samples_dir / 'package1', 'package1', '0.1', expected_editable=False
        )

def test_install_module(self):
        Installer.from_ini_path(samples_dir / 'module1_toml' / 'pyproject.toml').install_directly()
        assert_isfile(self.tmpdir / 'site-packages' / 'module1.py')
        assert_isdir(self.tmpdir / 'site-packages' / 'module1-0.1.dist-info')
        self._assert_direct_url(
            samples_dir / 'module1_toml', 'module1', '0.1', expected_editable=False
        )

def test_build_main(copy_sample):
    td = copy_sample('module1_toml')
    (td / '.git').mkdir()   # Fake a git repo

    with MockCommand('git', LIST_FILES_TEMPLATE.format(
            python=sys.executable, module='module1.py')):
        res = build.main(td / 'pyproject.toml')
    assert res.wheel.file.suffix == '.whl'
    assert res.sdist.file.name.endswith('.tar.gz')

    assert_isdir(td / 'dist')