How to use the testpath.assert_islink function in testpath

def test_symlink_package(self):
        if os.name == 'nt':
            raise SkipTest("symlink")
        Installer.from_ini_path(samples_dir / 'package1' / 'pyproject.toml', symlink=True).install()
        assert_islink(self.tmpdir / 'site-packages' / 'package1',
                      to=samples_dir / 'package1' / 'package1')
        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=True
        )

# Called by Installer._get_dirs() :
        script2 = ("#!{python}\n"
                   "import json, sys\n"
                   "json.dump({{'purelib': {purelib!r}, 'scripts': {scripts!r} }}, "
                   "sys.stdout)"
                  ).format(python=sys.executable,
                           purelib=str(self.tmpdir / 'site-packages2'),
                           scripts=str(self.tmpdir / 'scripts2'))

        with MockCommand('mock_python', content=script1):
            ins = Installer.from_ini_path(samples_dir / 'package1' / 'pyproject.toml', python='mock_python',
                      symlink=True)
        with MockCommand('mock_python', content=script2):
            ins.install()

        assert_islink(self.tmpdir / 'site-packages2' / 'package1',
                      to=samples_dir / 'package1' / 'package1')
        assert_isfile(self.tmpdir / 'scripts2' / 'pkg_script')
        with (self.tmpdir / 'scripts2' / 'pkg_script').open() as f:
            assert f.readline().strip() == "#!mock_python"