Rely on BTrees 4.8 and don't manually test for it as a Mapping.

CHANGES.rst

@@ -8,6 +8,8 @@
 
 - Add support for Python 3.9.
 
+- Depend on BTrees 4.8 and above. This simplifies externalization
+  checks. See `issue 111 <https://github.com/NextThought/nti.externalization/issues/111>`_.
 
 2.1.0 (2020-08-03)
 ==================

src/nti/externalization/externalization/externalizer.py

@@ -81,11 +81,10 @@
 
 #: The types that we will treat as mappings for externalization purposes. These
 #: all map onto a dict.
-MAPPING_TYPES = (
-    persistent.mapping.PersistentMapping,
-    BTrees.OOBTree.OOBTree,
-    Mapping
-)
+#: .. versionchanged:: 2.2.0
+#:     Now only the ABC Mapping is included. Previously BTrees and PersistentMapping
+#:     were special cased. But with BTrees 4.8.0, this is no longer needed.
+MAPPING_TYPES = (Mapping,)
 
 
 

src/nti/externalization/tests/test_externalization.py

@@ -821,6 +821,29 @@ def toExternalObject(self, *args, **kwargs):
         s = to_json_representation_externalized(result)
         assert_that(s, is_('{"Class": "O", "Creator": "creator"}'))
 
+    def test_externalize_OOBTree(self):
+        from BTrees import family64
+        bt = family64.OO.BTree()
+        bt['key'] = 'value'
+        result = toExternalObject(bt)
+        assert_that(result, is_(dict))
+        assert_that(result, is_({'Class': 'OOBTree', 'key': 'value'}))
+
+    def test_externalize_PersistentMapping(self):
+        from persistent.mapping import PersistentMapping
+        pm = PersistentMapping()
+        pm['key'] = 'value'
+        result = toExternalObject(pm)
+        assert_that(result, is_(dict))
+        assert_that(result, is_({'Class': 'PersistentMapping', 'key': 'value'}))
+
+    def test_externalize_IIBTree(self):
+        from BTrees import family64
+        bt = family64.II.BTree()
+        bt[1] = 2
+        result = toExternalObject(bt)
+        assert_that(result, is_(dict))
+        assert_that(result, is_({'Class': 'LLBTree', 1: 2}))
 
 @NoPickle
 class DoNotPickleMe(object):