chore: import upstream snapshot with attribution

easygraph/functions/core/tests/test_k_core.py

@@ -0,0 +1,101 @@
+import easygraph as eg
+import pytest
+
+from easygraph import k_core
+
+
+@pytest.mark.parametrize(
+    "edges,k",
+    [
+        ([(1, 2), (1, 3), (2, 3), (2, 4), (3, 4), (4, 5)], 2),
+        ([(1, 2), (1, 3), (2, 3), (2, 4), (3, 4), (4, 5)], 3),
+        ([(1, 2), (2, 3), (3, 4), (4, 5), (5, 6)], 2),
+        ([(1, 2), (2, 3), (3, 4), (4, 5), (5, 6)], 3),
+        ([(1, 2), (1, 3), (1, 4), (2, 3), (2, 4), (3, 4)], 1),
+    ],
+)
+def test_k_core(edges, k):
+    nx = pytest.importorskip("networkx")
+
+    from easygraph import Graph
+    from easygraph import k_core
+
+    G = Graph()
+    G_nx = nx.Graph()
+    G.add_edges_from(edges)
+    G_nx.add_edges_from(edges)
+
+    H = k_core(G)
+    H_nx = nx.core_number(G_nx)
+    assert H == list(H_nx.values())
+
+
+def test_k_core_empty_graph():
+    G = eg.Graph()
+    result = k_core(G)
+    assert result == []
+
+
+def test_k_core_single_node_isolated():
+    G = eg.Graph()
+    G.add_node(1)
+    result = k_core(G)
+    assert result == [0]
+
+
+def test_k_core_clique():
+    G = eg.complete_graph(5)  # Each node has degree 4
+    result = k_core(G)
+    assert set(result) == {4}
+
+
+def test_k_core_star_graph():
+    nx = pytest.importorskip("networkx")
+    G = eg.Graph()
+    G.add_node(0)
+    G.add_edges_from((0, i) for i in range(1, 6))
+    result = k_core(G)
+    G_nx = nx.Graph()
+    G_nx.add_node(0)
+    G_nx.add_edges_from((0, i) for i in range(1, 6))
+    expected = list(nx.core_number(G_nx).values())
+    assert sorted(result) == sorted(expected)
+
+
+def test_k_core_disconnected_components():
+    G = eg.Graph()
+    # Component 1: triangle
+    G.add_edges_from([(0, 1), (1, 2), (2, 0)])
+    # Component 2: line
+    G.add_edges_from([(3, 4)])
+    result = k_core(G)
+    core_component_1 = {result[i] for i in [0, 1, 2]}
+    core_component_2 = {result[i] for i in [3, 4]}
+    assert core_component_1 == {2}
+    assert core_component_2 == {1}
+
+
+def test_k_core_all_zero_core():
+    G = eg.path_graph(5)
+    result = k_core(G)
+    assert all(isinstance(v, int) or isinstance(v, float) for v in result)
+    assert max(result) <= 2
+
+
+def test_k_core_index_to_node_mapping_consistency():
+    G = eg.Graph()
+    edges = [(5, 10), (10, 15), (15, 20)]
+    G.add_edges_from(edges)
+    result = k_core(G)
+    for i, node in enumerate(G.index2node):
+        assert isinstance(result[i], (int, float))
+        deg_map = dict(G.degree())
+        if node in deg_map:
+            assert result[i] <= deg_map[node]
+
+
+def test_k_core_large_k():
+    G = eg.Graph()
+    G.add_edges_from([(1, 2), (2, 3)])
+    result = k_core(G)
+    assert max(result) <= 2