test: sound backoff-jitter assertions (per-delay band + non-overlapping growth) and scoped import-stub teardown in the pairing regression tests (F5 residual)

tests/test_config_flow_pairing.py

@@ -28,6 +28,20 @@ from nsh.const import (
 _KEY_PATH = "/tmp/nsh-test-adbkey"
 
 
+_STUB_NAMES = (
+    "voluptuous",
+    "homeassistant",
+    "homeassistant.config_entries",
+    "homeassistant.core",
+    "homeassistant.helpers",
+    "homeassistant.helpers.entity_registry",
+    "homeassistant.helpers.selector",
+    # Loaded execution runs beneath the stubs; never escape this file either.
+    "nsh.helpers",
+    "nsh.config_flow",
+)
+
+
 def _install_import_stubs() -> None:
     """Register import-time stand-ins for HA/voluptuous (idempotent)."""
     if sys.modules.get("voluptuous") is not None:
@@ -139,6 +153,25 @@ def _flow(user_input_host: str, monkeypatch=None):
     return flow
 
 
+@pytest.fixture(autouse=True)
+def scoped_stubs():
+    """Contain the import stubs to this module's tests (t7 INFO).
+
+    Snapshots every injected sys.modules entry and restores or removes it on
+    teardown, so later tests never observe the fake homeassistant/voluptuous
+    (nor the stub-loaded nsh.helpers/nsh.config_flow) modules.
+    """
+    snapshot = {name: sys.modules.get(name) for name in _STUB_NAMES}
+    _install_import_stubs()
+    yield
+    for name in _STUB_NAMES:
+        original = snapshot[name]
+        if original is None:
+            sys.modules.pop(name, None)
+        else:
+            sys.modules[name] = original
+
+
 @pytest.fixture
 def mocked_test_connect(monkeypatch):
     from nsh.connection import ShieldConnectionManager