test: scope nodes stub to a fixture to avoid sys.modules leakage

Per coderabbit feedback: replace the module-level sys.modules['nodes'] = stub
with a per-test fixture using monkeypatch.setitem so the fake module is torn
down after each test, and reload app.node_replace_manager so it picks up the
stub instead of any cached real import.

Amp-Thread-ID: https://ampcode.com/threads/T-019dd37c-4751-72ef-9927-3182b5825db0
Co-authored-by: Amp <amp@ampcode.com>

tests-unit/app_test/node_replace_manager_test.py

@@ -1,15 +1,29 @@
 """Tests for NodeReplaceManager registration behavior."""
+import importlib
 import sys
 import types
 
-# Stub `nodes` to avoid the heavy torch + ComfyUI import chain — register()
-# only touches its own dict, so it doesn't actually need NODE_CLASS_MAPPINGS.
-if "nodes" not in sys.modules:
-    _fake_nodes = types.ModuleType("nodes")
-    _fake_nodes.NODE_CLASS_MAPPINGS = {}
-    sys.modules["nodes"] = _fake_nodes
+import pytest
 
-from app.node_replace_manager import NodeReplaceManager  # noqa: E402
+
+@pytest.fixture
+def NodeReplaceManager(monkeypatch):
+    """Provide NodeReplaceManager with `nodes` stubbed.
+
+    `app.node_replace_manager` does `import nodes` at module level, which pulls in
+    torch + the full ComfyUI graph. register() doesn't actually need it, so we
+    stub `nodes` per-test (via monkeypatch so it's torn down) and reload the
+    module so it picks up the stub instead of any cached real import.
+    """
+    fake_nodes = types.ModuleType("nodes")
+    fake_nodes.NODE_CLASS_MAPPINGS = {}
+    monkeypatch.setitem(sys.modules, "nodes", fake_nodes)
+    monkeypatch.delitem(sys.modules, "app.node_replace_manager", raising=False)
+    module = importlib.import_module("app.node_replace_manager")
+    yield module.NodeReplaceManager
+    # Drop the freshly-imported module so the next test (or a later real import
+    # of `nodes`) starts from a clean slate.
+    sys.modules.pop("app.node_replace_manager", None)
 
 
 class FakeNodeReplace:
@@ -23,14 +37,14 @@ class FakeNodeReplace:
         self.output_mapping = output_mapping
 
 
-def test_register_adds_replacement():
+def test_register_adds_replacement(NodeReplaceManager):
     manager = NodeReplaceManager()
     manager.register(FakeNodeReplace(new_node_id="NewNode", old_node_id="OldNode"))
     assert manager.has_replacement("OldNode")
     assert len(manager.get_replacement("OldNode")) == 1
 
 
-def test_register_allows_multiple_alternatives_for_same_old_node():
+def test_register_allows_multiple_alternatives_for_same_old_node(NodeReplaceManager):
     """Different new_node_ids for the same old_node_id should all be kept."""
     manager = NodeReplaceManager()
     manager.register(FakeNodeReplace(new_node_id="AltA", old_node_id="OldNode"))
@@ -40,7 +54,7 @@ def test_register_allows_multiple_alternatives_for_same_old_node():
     assert {r.new_node_id for r in replacements} == {"AltA", "AltB"}
 
 
-def test_register_is_idempotent_for_duplicate_pair():
+def test_register_is_idempotent_for_duplicate_pair(NodeReplaceManager):
     """Re-registering the same (old_node_id, new_node_id) should be a no-op."""
     manager = NodeReplaceManager()
     manager.register(FakeNodeReplace(new_node_id="NewNode", old_node_id="OldNode"))
@@ -49,7 +63,7 @@ def test_register_is_idempotent_for_duplicate_pair():
     assert len(manager.get_replacement("OldNode")) == 1
 
 
-def test_register_idempotent_preserves_first_registration():
+def test_register_idempotent_preserves_first_registration(NodeReplaceManager):
     """First registration wins; later duplicates with different mappings are ignored."""
     manager = NodeReplaceManager()
     first = FakeNodeReplace(
@@ -67,7 +81,7 @@ def test_register_idempotent_preserves_first_registration():
     assert replacements[0] is first
 
 
-def test_register_dedupe_does_not_affect_other_old_nodes():
+def test_register_dedupe_does_not_affect_other_old_nodes(NodeReplaceManager):
     manager = NodeReplaceManager()
     manager.register(FakeNodeReplace(new_node_id="NewA", old_node_id="OldA"))
     manager.register(FakeNodeReplace(new_node_id="NewA", old_node_id="OldA"))