Refs #30179 -- Moved topological sort functions to django.utils.

tests/utils_tests/test_topological_sort.py

@@ -0,0 +1,24 @@
+from django.test import SimpleTestCase
+from django.utils.topological_sort import (
+    CyclicDependencyError, stable_topological_sort, topological_sort_as_sets,
+)
+
+
+class TopologicalSortTests(SimpleTestCase):
+
+    def test_basic(self):
+        dependency_graph = {
+            1: {2, 3},
+            2: set(),
+            3: set(),
+            4: {5, 6},
+            5: set(),
+            6: {5},
+        }
+        self.assertEqual(list(topological_sort_as_sets(dependency_graph)), [{2, 3, 5}, {1, 6}, {4}])
+        self.assertEqual(stable_topological_sort([1, 2, 3, 4, 5, 6], dependency_graph), [2, 3, 5, 1, 6, 4])
+
+    def test_cyclic_dependency(self):
+        msg = 'Cyclic dependency in graph: (1, {2}), (2, {1})'
+        with self.assertRaisesMessage(CyclicDependencyError, msg):
+            list(topological_sort_as_sets({1: {2}, 2: {1}}))