DM-41846: Add ability to reset storage class factory

python/lsst/daf/butler/_storage_class.py

@@ -661,7 +661,7 @@ def __str__(self) -> str:
 
 StorageClasses
 --------------
-{sep.join(f"{s}: {self._storageClasses[s]}" for s in self._storageClasses)}
+{sep.join(f"{s}: {self._storageClasses[s]!r}" for s in sorted(self._storageClasses))}
 """
 
     def __contains__(self, storageClassOrName: StorageClass | str) -> bool:
@@ -989,3 +989,13 @@ def _unregisterStorageClass(self, storageClassName: str) -> None:
         functionality and it is not expected to be required for normal usage.
         """
         del self._storageClasses[storageClassName]
+
+    def reset(self) -> None:
+        """Remove all storage class entries from factory and reset to
+        initial state.
+
+        This is useful for test code where a known start state is useful.
+        """
+        self._storageClasses.clear()
+        # Seed with the default config.
+        self.addFromConfig(StorageClassConfig())

tests/test_storageClass.py

@@ -243,6 +243,12 @@ def testRegistry(self):
         # Check you can silently insert something that is already there
         factory.registerStorageClass(newclass3)
 
+        # Reset the factory and check that default items are present
+        # but the new ones are not.
+        factory.reset()
+        self.assertNotIn(newclass3.name, factory)
+        self.assertIn("StructuredDataDict", factory)
+
     def testFactoryFind(self):
         # Finding a storage class can involve doing lots of slow imports so
         # this is a separate test.