diff --git a/Lib/collections/__init__.py b/Lib/collections/__init__.py
index 3d3bbd7a3..803de0c67 100644
--- a/Lib/collections/__init__.py
+++ b/Lib/collections/__init__.py
@@ -57,8 +57,7 @@ except ImportError:
 try:
     from _collections import defaultdict
 except ImportError:
-    # TODO: RUSTPYTHON - implement defaultdict in Rust
-    from ._defaultdict import defaultdict
+    pass
 
 heapq = None  # Lazily imported
 
diff --git a/Lib/collections/_defaultdict.py b/Lib/collections/_defaultdict.py
deleted file mode 100644
index b9c6c4961..000000000
--- a/Lib/collections/_defaultdict.py
+++ /dev/null
@@ -1,58 +0,0 @@
-from reprlib import recursive_repr as _recursive_repr
-
-class defaultdict(dict):
-    def __init__(self, *args, **kwargs):
-        if len(args) >= 1:
-            default_factory = args[0]
-            if default_factory is not None and not callable(default_factory):
-                raise TypeError("first argument must be callable or None")
-            args = args[1:]
-        else:
-            default_factory = None
-        super().__init__(*args, **kwargs)
-        self.default_factory = default_factory
-
-    def __missing__(self, key):
-        if self.default_factory is not None:
-            val = self.default_factory()
-        else:
-            raise KeyError(key)
-        self[key] = val
-        return val
-
-    @_recursive_repr()
-    def __repr_factory(factory):
-        return repr(factory)
-
-    def __repr__(self):
-        return f"{type(self).__name__}({defaultdict.__repr_factory(self.default_factory)}, {dict.__repr__(self)})"
-
-    def copy(self):
-        return type(self)(self.default_factory, self)
-
-    __copy__ = copy
-
-    def __reduce__(self):
-        if self.default_factory is not None:
-            args = self.default_factory,
-        else:
-            args = ()
-        return type(self), args, None, None, iter(self.items())
-
-    def __or__(self, other):
-        if not isinstance(other, dict):
-            return NotImplemented
-
-        new = defaultdict(self.default_factory, self)
-        new.update(other)
-        return new
-
-    def __ror__(self, other):
-        if not isinstance(other, dict):
-            return NotImplemented
-
-        new = defaultdict(self.default_factory, other)
-        new.update(self)
-        return new
-
-defaultdict.__module__ = 'collections'
diff --git a/Lib/test/mapping_tests.py b/Lib/test/mapping_tests.py
index 53f29f605..20306e152 100644
--- a/Lib/test/mapping_tests.py
+++ b/Lib/test/mapping_tests.py
@@ -1,7 +1,7 @@
 # tests common to dict and UserDict
 import unittest
 import collections
-import sys
+from test import support
 
 
 class BasicTestMappingProtocol(unittest.TestCase):
@@ -70,8 +70,8 @@ class BasicTestMappingProtocol(unittest.TestCase):
         if not d: self.fail("Full mapping must compare to True")
         # keys(), items(), iterkeys() ...
         def check_iterandlist(iter, lst, ref):
-            self.assertTrue(hasattr(iter, '__next__'))
-            self.assertTrue(hasattr(iter, '__iter__'))
+            self.assertHasAttr(iter, '__next__')
+            self.assertHasAttr(iter, '__iter__')
             x = list(iter)
             self.assertTrue(set(x)==set(lst)==set(ref))
         check_iterandlist(iter(d.keys()), list(d.keys()),
@@ -448,7 +448,7 @@ class TestMappingProtocol(BasicTestMappingProtocol):
         class Exc(Exception): pass
 
         class baddict1(self.type2test):
-            def __init__(self):
+            def __init__(self, *args, **kwargs):
                 raise Exc()
 
         self.assertRaises(Exc, baddict1.fromkeys, [1])
@@ -595,12 +595,14 @@ class TestHashMappingProtocol(TestMappingProtocol):
         d = self._empty_mapping()
         d[1] = 1
         try:
+            count = 0
             for i in d:
                 d[i+1] = 1
+                if count >= 1:
+                    self.fail("changing dict size during iteration doesn't raise Error")
+                count += 1
         except RuntimeError:
             pass
-        else:
-            self.fail("changing dict size during iteration doesn't raise Error")
 
     def test_repr(self):
         d = self._empty_mapping()
@@ -620,9 +622,12 @@ class TestHashMappingProtocol(TestMappingProtocol):
         d = self._full_mapping({1: BadRepr()})
         self.assertRaises(Exc, repr, d)
 
+    @support.skip_wasi_stack_overflow()
+    @support.skip_emscripten_stack_overflow()
+    @support.skip_if_sanitizer("requires deep stack", ub=True)
     def test_repr_deep(self):
         d = self._empty_mapping()
-        for i in range(sys.getrecursionlimit() + 100):
+        for i in range(support.exceeds_recursion_limit()):
             d0 = d
             d = self._empty_mapping()
             d[1] = d0