How to use the tskit.load_text function in tskit

def test_empty_files_sequence_length(self):
        nodes_file = six.StringIO("is_sample\ttime\n")
        edges_file = six.StringIO("left\tright\tparent\tchild\n")
        sites_file = six.StringIO("position\tancestral_state\n")
        mutations_file = six.StringIO("site\tnode\tderived_state\n")
        ts = tskit.load_text(
            nodes=nodes_file, edges=edges_file, sites=sites_file,
            mutations=mutations_file, sequence_length=100)
        self.assertEqual(ts.sequence_length, 100)
        self.assertEqual(ts.num_nodes, 0)
        self.assertEqual(ts.num_edges, 0)
        self.assertEqual(ts.num_sites, 0)
        self.assertEqual(ts.num_edges, 0)

0   1           0
        1   1           0
        2   1           0
        3   1           2
        """)
        edges = six.StringIO("""\
        left    right   parent  child
        0       1       3       0
        0       1       3       1
        0       1       3       2
        """)
        tree = (
            "  3  \n"
            "┏━╋━┓\n"
            "0 1 2\n")
        ts = tskit.load_text(nodes, edges, strict=False)
        t = next(ts.trees())
        drawn = t.draw(format="unicode")
        self.verify_text_rendering(drawn, tree)

id      is_sample   time
        0       1           0
        """)
        edges = six.StringIO("""\
        left    right   parent  child
        """)
        sites = six.StringIO("""\
        position    ancestral_state
        0.1     0
        """)
        mutations = six.StringIO("""\
        site    node    derived_state   parent
        1       0       1               -2
        """)
        self.assertRaises(
            _tskit.LibraryError, tskit.load_text,
            nodes=nodes, edges=edges, sites=sites, mutations=mutations,
            sequence_length=1, strict=False)

1   0.3         0
        2   0.9         0
        """)
        mutations = six.StringIO("""\
        site    node    derived_state   parent
        0       0       1               -1
        0       0       2               0
        0       0       0               1
        0       1       2               -1
        1       1       1               -1
        1       2       1               -1
        2       4       1               -1
        2       1       2               6
        2       2       3               6
        """)
        ts = tskit.load_text(
            nodes=nodes, edges=edges, sites=sites, mutations=mutations, strict=False)
        site_tsc = tskit.SiteStatCalculator(ts)
        py_site_tsc = PythonSiteStatCalculator(ts)

        # Y3:
        site_tsc_Y = site_tsc.Y3([[0], [1], [2]], [0.0, 1.0])[0][0]
        py_site_tsc_Y = py_site_tsc.Y3([0], [1], [2], 0.0, 1.0)
        self.assertAlmostEqual(site_tsc_Y, site_true_Y)
        self.assertAlmostEqual(py_site_tsc_Y, site_true_Y)

0   1           0
        1   1           1
        2   1           2
        """)
        edges = six.StringIO("""\
        left    right   parent  child
        0       1       1       0
        0       1       2       1
        """)
        tree = (
            "2\n"
            "┃\n"
            "1\n"
            "┃\n"
            "0\n")
        ts = tskit.load_text(nodes, edges, strict=False)
        t = next(ts.trees())
        drawn = t.draw(format="unicode")
        self.verify_text_rendering(drawn, tree)

2   1           2
        3   1           1
        4   1           4
        5   1           5
        6   1           7
        """)
        edges = six.StringIO("""\
        left    right   parent  child
        0       1       6       0
        0       1       6       1
        0       1       6       2
        0       1       6       3
        0       1       6       4
        0       1       6       5
        """)
        ts = tskit.load_text(nodes, edges, strict=False)
        t = next(ts.trees())
        text = t.draw(format=self.drawing_format)
        self.verify_basic_text(text)

""")
        sites = six.StringIO("""\
        position    ancestral_state
        0.1     0
        0.2     0
        """)
        mutations = six.StringIO("""\
        site    node    derived_state   parent
        1       0       1               -1
        1       0       0               0
        1       0       1               1
        0       0       1               -1
        0       0       0               3
        0       0       1               4
        """)
        ts = tskit.load_text(
            nodes=nodes, edges=edges, sites=sites, mutations=mutations,
            sequence_length=1, strict=False)
        # Load text automatically calls sort tables, so we can test the
        # output directly.
        sites = ts.tables.sites
        mutations = ts.tables.mutations
        self.assertEqual(len(sites), 2)
        self.assertEqual(len(mutations), 6)
        self.assertEqual(list(mutations.site), [0, 0, 0, 1, 1, 1])
        self.assertEqual(list(mutations.node), [0, 0, 0, 0, 0, 0])
        self.assertEqual(list(mutations.parent), [-1, 0, 1, -1, 3, 4])

def test_empty_files(self):
        nodes_file = six.StringIO("is_sample\ttime\n")
        edges_file = six.StringIO("left\tright\tparent\tchild\n")
        sites_file = six.StringIO("position\tancestral_state\n")
        mutations_file = six.StringIO("site\tnode\tderived_state\n")
        self.assertRaises(
            _tskit.LibraryError, tskit.load_text,
            nodes=nodes_file, edges=edges_file, sites=sites_file,
            mutations=mutations_file)

1       1           0
    2       1           0
    3       1           0
    4       1           0
    5       0           1
    6       0           2
    7       0           3
    """
    edges = """\
    left    right   parent  child
    0       1       5       0,1,2
    0       1       6       3,4
    0       1       7       5,6
    """
    # NB same tree as used above, and we're using the same diagram.
    ts = tskit.load_text(
        nodes=io.StringIO(nodes), edges=io.StringIO(edges), strict=False)
    tree = ts.first()

    for order in ["preorder", "inorder", "postorder"]:
        print(f"{order}:\t", list(tree.nodes(order=order)))


    total_branch_length = sum(tree.branch_length(u) for u in tree.nodes())
    print(total_branch_length, tree.total_branch_length)

    for u in tree.samples():
        path = []
        v = u
        while v != tskit.NULL:
            path.append(v)
            v = tree.parent(v)