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diff --git a/.venv/lib/python3.12/site-packages/networkx/algorithms/approximation/tests/test_steinertree.py b/.venv/lib/python3.12/site-packages/networkx/algorithms/approximation/tests/test_steinertree.py
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+++ b/.venv/lib/python3.12/site-packages/networkx/algorithms/approximation/tests/test_steinertree.py
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+import pytest
+
+import networkx as nx
+from networkx.algorithms.approximation.steinertree import (
+    _remove_nonterminal_leaves,
+    metric_closure,
+    steiner_tree,
+)
+from networkx.utils import edges_equal
+
+
+class TestSteinerTree:
+    @classmethod
+    def setup_class(cls):
+        G1 = nx.Graph()
+        G1.add_edge(1, 2, weight=10)
+        G1.add_edge(2, 3, weight=10)
+        G1.add_edge(3, 4, weight=10)
+        G1.add_edge(4, 5, weight=10)
+        G1.add_edge(5, 6, weight=10)
+        G1.add_edge(2, 7, weight=1)
+        G1.add_edge(7, 5, weight=1)
+
+        G2 = nx.Graph()
+        G2.add_edge(0, 5, weight=6)
+        G2.add_edge(1, 2, weight=2)
+        G2.add_edge(1, 5, weight=3)
+        G2.add_edge(2, 4, weight=4)
+        G2.add_edge(3, 5, weight=5)
+        G2.add_edge(4, 5, weight=1)
+
+        G3 = nx.Graph()
+        G3.add_edge(1, 2, weight=8)
+        G3.add_edge(1, 9, weight=3)
+        G3.add_edge(1, 8, weight=6)
+        G3.add_edge(1, 10, weight=2)
+        G3.add_edge(1, 14, weight=3)
+        G3.add_edge(2, 3, weight=6)
+        G3.add_edge(3, 4, weight=3)
+        G3.add_edge(3, 10, weight=2)
+        G3.add_edge(3, 11, weight=1)
+        G3.add_edge(4, 5, weight=1)
+        G3.add_edge(4, 11, weight=1)
+        G3.add_edge(5, 6, weight=4)
+        G3.add_edge(5, 11, weight=2)
+        G3.add_edge(5, 12, weight=1)
+        G3.add_edge(5, 13, weight=3)
+        G3.add_edge(6, 7, weight=2)
+        G3.add_edge(6, 12, weight=3)
+        G3.add_edge(6, 13, weight=1)
+        G3.add_edge(7, 8, weight=3)
+        G3.add_edge(7, 9, weight=3)
+        G3.add_edge(7, 11, weight=5)
+        G3.add_edge(7, 13, weight=2)
+        G3.add_edge(7, 14, weight=4)
+        G3.add_edge(8, 9, weight=2)
+        G3.add_edge(9, 14, weight=1)
+        G3.add_edge(10, 11, weight=2)
+        G3.add_edge(10, 14, weight=1)
+        G3.add_edge(11, 12, weight=1)
+        G3.add_edge(11, 14, weight=7)
+        G3.add_edge(12, 14, weight=3)
+        G3.add_edge(12, 15, weight=1)
+        G3.add_edge(13, 14, weight=4)
+        G3.add_edge(13, 15, weight=1)
+        G3.add_edge(14, 15, weight=2)
+
+        cls.G1 = G1
+        cls.G2 = G2
+        cls.G3 = G3
+        cls.G1_term_nodes = [1, 2, 3, 4, 5]
+        cls.G2_term_nodes = [0, 2, 3]
+        cls.G3_term_nodes = [1, 3, 5, 6, 8, 10, 11, 12, 13]
+
+        cls.methods = ["kou", "mehlhorn"]
+
+    def test_connected_metric_closure(self):
+        G = self.G1.copy()
+        G.add_node(100)
+        pytest.raises(nx.NetworkXError, metric_closure, G)
+
+    def test_metric_closure(self):
+        M = metric_closure(self.G1)
+        mc = [
+            (1, 2, {"distance": 10, "path": [1, 2]}),
+            (1, 3, {"distance": 20, "path": [1, 2, 3]}),
+            (1, 4, {"distance": 22, "path": [1, 2, 7, 5, 4]}),
+            (1, 5, {"distance": 12, "path": [1, 2, 7, 5]}),
+            (1, 6, {"distance": 22, "path": [1, 2, 7, 5, 6]}),
+            (1, 7, {"distance": 11, "path": [1, 2, 7]}),
+            (2, 3, {"distance": 10, "path": [2, 3]}),
+            (2, 4, {"distance": 12, "path": [2, 7, 5, 4]}),
+            (2, 5, {"distance": 2, "path": [2, 7, 5]}),
+            (2, 6, {"distance": 12, "path": [2, 7, 5, 6]}),
+            (2, 7, {"distance": 1, "path": [2, 7]}),
+            (3, 4, {"distance": 10, "path": [3, 4]}),
+            (3, 5, {"distance": 12, "path": [3, 2, 7, 5]}),
+            (3, 6, {"distance": 22, "path": [3, 2, 7, 5, 6]}),
+            (3, 7, {"distance": 11, "path": [3, 2, 7]}),
+            (4, 5, {"distance": 10, "path": [4, 5]}),
+            (4, 6, {"distance": 20, "path": [4, 5, 6]}),
+            (4, 7, {"distance": 11, "path": [4, 5, 7]}),
+            (5, 6, {"distance": 10, "path": [5, 6]}),
+            (5, 7, {"distance": 1, "path": [5, 7]}),
+            (6, 7, {"distance": 11, "path": [6, 5, 7]}),
+        ]
+        assert edges_equal(list(M.edges(data=True)), mc)
+
+    def test_steiner_tree(self):
+        valid_steiner_trees = [
+            [
+                [
+                    (1, 2, {"weight": 10}),
+                    (2, 3, {"weight": 10}),
+                    (2, 7, {"weight": 1}),
+                    (3, 4, {"weight": 10}),
+                    (5, 7, {"weight": 1}),
+                ],
+                [
+                    (1, 2, {"weight": 10}),
+                    (2, 7, {"weight": 1}),
+                    (3, 4, {"weight": 10}),
+                    (4, 5, {"weight": 10}),
+                    (5, 7, {"weight": 1}),
+                ],
+                [
+                    (1, 2, {"weight": 10}),
+                    (2, 3, {"weight": 10}),
+                    (2, 7, {"weight": 1}),
+                    (4, 5, {"weight": 10}),
+                    (5, 7, {"weight": 1}),
+                ],
+            ],
+            [
+                [
+                    (0, 5, {"weight": 6}),
+                    (1, 2, {"weight": 2}),
+                    (1, 5, {"weight": 3}),
+                    (3, 5, {"weight": 5}),
+                ],
+                [
+                    (0, 5, {"weight": 6}),
+                    (4, 2, {"weight": 4}),
+                    (4, 5, {"weight": 1}),
+                    (3, 5, {"weight": 5}),
+                ],
+            ],
+            [
+                [
+                    (1, 10, {"weight": 2}),
+                    (3, 10, {"weight": 2}),
+                    (3, 11, {"weight": 1}),
+                    (5, 12, {"weight": 1}),
+                    (6, 13, {"weight": 1}),
+                    (8, 9, {"weight": 2}),
+                    (9, 14, {"weight": 1}),
+                    (10, 14, {"weight": 1}),
+                    (11, 12, {"weight": 1}),
+                    (12, 15, {"weight": 1}),
+                    (13, 15, {"weight": 1}),
+                ]
+            ],
+        ]
+        for method in self.methods:
+            for G, term_nodes, valid_trees in zip(
+                [self.G1, self.G2, self.G3],
+                [self.G1_term_nodes, self.G2_term_nodes, self.G3_term_nodes],
+                valid_steiner_trees,
+            ):
+                S = steiner_tree(G, term_nodes, method=method)
+                assert any(
+                    edges_equal(list(S.edges(data=True)), valid_tree)
+                    for valid_tree in valid_trees
+                )
+
+    def test_multigraph_steiner_tree(self):
+        G = nx.MultiGraph()
+        G.add_edges_from(
+            [
+                (1, 2, 0, {"weight": 1}),
+                (2, 3, 0, {"weight": 999}),
+                (2, 3, 1, {"weight": 1}),
+                (3, 4, 0, {"weight": 1}),
+                (3, 5, 0, {"weight": 1}),
+            ]
+        )
+        terminal_nodes = [2, 4, 5]
+        expected_edges = [
+            (2, 3, 1, {"weight": 1}),  # edge with key 1 has lower weight
+            (3, 4, 0, {"weight": 1}),
+            (3, 5, 0, {"weight": 1}),
+        ]
+        for method in self.methods:
+            S = steiner_tree(G, terminal_nodes, method=method)
+            assert edges_equal(S.edges(data=True, keys=True), expected_edges)
+
+    def test_remove_nonterminal_leaves(self):
+        G = nx.path_graph(10)
+        _remove_nonterminal_leaves(G, [4, 5, 6])
+
+        assert list(G) == [4, 5, 6]  # only the terminal nodes are left
+
+
+@pytest.mark.parametrize("method", ("kou", "mehlhorn"))
+def test_steiner_tree_weight_attribute(method):
+    G = nx.star_graph(4)
+    # Add an edge attribute that is named something other than "weight"
+    nx.set_edge_attributes(G, {e: 10 for e in G.edges}, name="distance")
+    H = nx.approximation.steiner_tree(G, [1, 3], method=method, weight="distance")
+    assert nx.utils.edges_equal(H.edges, [(0, 1), (0, 3)])
+
+
+@pytest.mark.parametrize("method", ("kou", "mehlhorn"))
+def test_steiner_tree_multigraph_weight_attribute(method):
+    G = nx.cycle_graph(3, create_using=nx.MultiGraph)
+    nx.set_edge_attributes(G, {e: 10 for e in G.edges}, name="distance")
+    G.add_edge(2, 0, distance=5)
+    H = nx.approximation.steiner_tree(G, list(G), method=method, weight="distance")
+    assert len(H.edges) == 2 and H.has_edge(2, 0, key=1)
+    assert sum(dist for *_, dist in H.edges(data="distance")) == 15
+
+
+@pytest.mark.parametrize("method", (None, "mehlhorn", "kou"))
+def test_steiner_tree_methods(method):
+    G = nx.star_graph(4)
+    expected = nx.Graph([(0, 1), (0, 3)])
+    st = nx.approximation.steiner_tree(G, [1, 3], method=method)
+    assert nx.utils.edges_equal(st.edges, expected.edges)
+
+
+def test_steiner_tree_method_invalid():
+    G = nx.star_graph(4)
+    with pytest.raises(
+        ValueError, match="invalid_method is not a valid choice for an algorithm."
+    ):
+        nx.approximation.steiner_tree(G, terminal_nodes=[1, 3], method="invalid_method")
+
+
+def test_steiner_tree_remove_non_terminal_leaves_self_loop_edges():
+    # To verify that the last step of the steiner tree approximation
+    # behaves in the case where a non-terminal leaf has a self loop edge
+    G = nx.path_graph(10)
+
+    # Add self loops to the terminal nodes
+    G.add_edges_from([(2, 2), (3, 3), (4, 4), (7, 7), (8, 8)])
+
+    # Remove non-terminal leaves
+    _remove_nonterminal_leaves(G, [4, 5, 6, 7])
+
+    # The terminal nodes should be left
+    assert list(G) == [4, 5, 6, 7]  # only the terminal nodes are left
+
+
+def test_steiner_tree_non_terminal_leaves_multigraph_self_loop_edges():
+    # To verify that the last step of the steiner tree approximation
+    # behaves in the case where a non-terminal leaf has a self loop edge
+    G = nx.MultiGraph()
+    G.add_edges_from([(i, i + 1) for i in range(10)])
+    G.add_edges_from([(2, 2), (3, 3), (4, 4), (4, 4), (7, 7)])
+
+    # Remove non-terminal leaves
+    _remove_nonterminal_leaves(G, [4, 5, 6, 7])
+
+    # Only the terminal nodes should be left
+    assert list(G) == [4, 5, 6, 7]