improved tests

tests/test_example_build-graph.py

@@ -0,0 +1,76 @@
+import pytest
+
+from daglib.dag import DAG
+from daglib.operations import all_nodes
+
+
+@pytest.fixture
+def build_graph() -> DAG[str]:
+    graph = DAG[str]()
+    graph.add_edge("checkout", "compile")
+    graph.add_edge("toolchain", "compile")
+    graph.add_edge("compile", "package")
+    graph.add_edge("package", "deploy")
+    return graph
+
+
+def test_subgraph_reverse_mutation_preserves_parent_edge_consistency(build_graph: DAG[str]) -> None:
+    assert "compile" in build_graph["toolchain"]
+    assert "toolchain" in build_graph.reverse["compile"]
+
+    pipeline = build_graph.subgraph("checkout")
+    pipeline.reverse["compile"].discard("toolchain")
+
+    forward_has_edge = "compile" in build_graph["toolchain"]
+    reverse_has_edge = "toolchain" in build_graph.reverse["compile"]
+    assert forward_has_edge == reverse_has_edge, "Subgraph mutation desynchronized the parent DAG's edge indexes"
+    assert forward_has_edge
+
+
+def test_subgraph_reverse_mutation_preserves_parent_topological_dependencies(build_graph: DAG[str]) -> None:
+    assert "toolchain" in build_graph.topo_sort()
+
+    pipeline = build_graph.subgraph("checkout")
+    pipeline.reverse["compile"].discard("toolchain")
+
+    assert "compile" in build_graph["toolchain"]
+    order = build_graph.topo_sort()
+    assert "toolchain" in order, "Topological sorting omitted a node with an outgoing edge in the parent DAG"
+    assert order.index("toolchain") < order.index("compile")
+
+
+def test_build_subgraph_excludes_external_dependencies(build_graph: DAG[str]) -> None:
+    pipeline = build_graph.subgraph("checkout")
+
+    assert all_nodes(pipeline) == {"checkout", "compile", "package", "deploy"}
+    assert set(pipeline.reverse["compile"]) == {"checkout"}
+    assert len(pipeline) == 3
+    order = pipeline.topo_sort()
+    assert set(order) == all_nodes(pipeline)
+    assert order.index("checkout") < order.index("compile") < order.index("package") < order.index("deploy")
+
+
+@pytest.mark.parametrize("mutate_parent", [False, True], ids=["child-mutation", "parent-mutation"])
+@pytest.mark.parametrize("mutation", ["add", "remove", "reverse-remove", "discard-node"])
+def test_build_subgraph_mutations_are_isolated(build_graph: DAG[str], mutate_parent: bool, mutation: str) -> None:
+    pipeline = build_graph.subgraph("checkout")
+    changed, protected = (build_graph, pipeline) if mutate_parent else (pipeline, build_graph)
+    successors = {node: set(protected[node]) for node in protected}
+    predecessors = {node: set(protected.reverse[node]) for node in protected.reverse}
+
+    match mutation:
+        case "add":
+            changed["package"].add("publish")
+        case "remove":
+            changed["compile"].discard("package")
+        case "reverse-remove":
+            changed.reverse["compile"].discard("checkout")
+        case "discard-node":
+            changed.discard_node("compile")
+
+    assert {node: set(protected[node]) for node in protected} == successors
+    assert {node: set(protected.reverse[node]) for node in protected.reverse} == predecessors
+    for graph in (changed, protected):
+        forward_edges = {(source, target) for source in graph for target in graph[source]}
+        reverse_edges = {(source, target) for target in graph.reverse for source in graph.reverse[target]}
+        assert forward_edges == reverse_edges