subgraph test

tests/test_dag.py

@@ -12,6 +12,10 @@ class TestDAGInit:
         g = DAG()
         assert len(g) == 0
 
+    def test_reverse(self) -> None:
+        g = DAG()
+        assert len(g.reverse) == 0
+
     def test_default_callbacks_none(self) -> None:
         g = DAG()
         assert g.on_add is None
@@ -310,3 +314,17 @@ class TestDAGComplexScenarios:
         assert 2 in g[1]
         assert 4 in g[2]
         assert len(g) == 3
+
+    def test_subgraphs(self) -> None:
+        g = DAG[str]()
+        g["A"] += "B"
+        g["B"] += "C"
+        g["B"] += "D"
+        g["D"] += "E"
+        g["E"] += "F"
+        assert len(g) == 5
+
+        sub = g.subgraph("D")
+        assert len(sub) == 2
+        assert set(sub["D"]) == {"E"}
+        assert set(sub["E"]) == {"F"}