How to use the flit.install.Installer.from_ini_path function in flit

def test_pip_install(self):
        ins = Installer.from_ini_path(samples_dir / 'package1' / 'pyproject.toml', python='mock_python',
                        user=False)

        with MockCommand('mock_python') as mock_py:
            ins.install()

        calls = mock_py.get_calls()
        assert len(calls) == 1
        cmd = calls[0]['argv']
        assert cmd[1:4] == ['-m', 'pip', 'install']
        assert cmd[4].endswith('package1')

def test_install_requires(self):
        ins = Installer.from_ini_path(samples_dir / 'requires-requests.toml',
                        user=False, python='mock_python')

        with MockCommand('mock_python') as mockpy:
            ins.install_requirements()
        calls = mockpy.get_calls()
        assert len(calls) == 1
        assert calls[0]['argv'][1:5] == ['-m', 'pip', 'install', '-r']

def test_entry_points(self):
        Installer.from_ini_path(samples_dir / 'entrypoints_valid' / 'pyproject.toml').install_directly()
        assert_isfile(self.tmpdir / 'site-packages' / 'package1-0.1.dist-info' / 'entry_points.txt')

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_extras_error(self):
        with pytest.raises(DependencyError):
            Installer.from_ini_path(samples_dir / 'requires-requests.toml',
                            user=False, deps='none', extras='dev')

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_pth_package(self):
        Installer.from_ini_path(samples_dir / 'package1' / 'pyproject.toml', pth=True).install()
        assert_isfile(self.tmpdir / 'site-packages' / 'package1.pth')
        with open(str(self.tmpdir / 'site-packages' / 'package1.pth')) as f:
            assert f.read() == str(samples_dir / 'package1')
        assert_isfile(self.tmpdir / 'scripts' / 'pkg_script')
        self._assert_direct_url(
            samples_dir / 'package1', 'package1', '0.1', expected_editable=True
        )

gen_setup_py=args.setup_py)
        except(common.NoDocstringError, common.VCSError, common.NoVersionError) as e:
            sys.exit(e.args[0])
    elif args.subcmd == 'publish':
        if args.deprecated_repository:
            log.warning("Passing --repository before the 'upload' subcommand is deprecated: pass it after")
        repository = args.repository or args.deprecated_repository
        from .upload import main
        main(args.ini_file, repository, formats=set(args.format or []),
                gen_setup_py=args.setup_py)

    elif args.subcmd == 'install':
        from .install import Installer
        try:
            python = find_python_executable(args.python)
            Installer.from_ini_path(args.ini_file, user=args.user, python=python,
                      symlink=args.symlink, deps=args.deps, extras=args.extras,
                      pth=args.pth_file).install()
        except (ConfigError, PythonNotFoundError, common.NoDocstringError, common.NoVersionError) as e:
            sys.exit(e.args[0])

    elif args.subcmd == 'init':
        from .init import TerminalIniter
        TerminalIniter().initialise()
    else:
        ap.print_help()
        sys.exit(1)