diff --git a/detect_secrets/settings.py b/detect_secrets/settings.py
index e4bd9d8b..97020000 100644
--- a/detect_secrets/settings.py
+++ b/detect_secrets/settings.py
@@ -71,6 +71,7 @@ def default_settings() -> Generator['Settings', None, None]:
             for plugin_type in get_mapping_from_secret_type_to_class().values()
         ],
     }) as settings:
+        get_mapping_from_secret_type_to_class.cache_clear()
         yield settings
 
 
diff --git a/testing/plugins.py b/testing/plugins.py
index 5a5957fc..8c08dfec 100644
--- a/testing/plugins.py
+++ b/testing/plugins.py
@@ -2,6 +2,7 @@
 from contextlib import contextmanager
 from typing import Any
 from typing import Generator
+from unittest import mock
 
 from detect_secrets.core.plugins import Plugin
 from detect_secrets.core.plugins.util import get_mapping_from_secret_type_to_class
@@ -19,9 +20,16 @@ def get_instance(*args: Any, **kwargs: Any) -> Plugin:
     # registered plugins, this shimmed function will be known as the underlying plugin class.
     get_instance.__name__ = plugin.__class__.__name__
 
+    get_mapping_from_secret_type_to_class.cache_clear()
+    mapping = get_mapping_from_secret_type_to_class()
+    mapping[plugin.secret_type] =  get_instance  # type: ignore
+
     try:
-        get_mapping_from_secret_type_to_class()[plugin.secret_type] = get_instance  # type: ignore
-        yield
+        with mock.patch(
+            'detect_secrets.core.plugins.util.get_mapping_from_secret_type_to_class',
+            return_value = mapping
+        ):
+            yield
     finally:
         # On next run, it should re-initialize to base state.
         get_mapping_from_secret_type_to_class.cache_clear()