--- /dev/null
+++ libmalloc/libmalloc-646.40.3/tests/add_xzone_tests.py
@@ -0,0 +1,134 @@
+#!/usr/bin/env python3
+
+import argparse
+import copy
+import plistlib
+from os.path import exists
+
+def create_xzone_test(test, nano_on_xzone):
+    xzone_test = copy.deepcopy(test)
+
+    extension = 'nano-on-xzone' if nano_on_xzone else 'xzone'
+
+    if 'TestName' in xzone_test:
+        orig_name = xzone_test['TestName']
+        xzone_test['TestName'] = orig_name + '.' + extension
+
+    if 'CanonicalName' in xzone_test:
+        # The CanonicalName for darwintests has a .<arch> suffix that we
+        # want to keep at the end, so insert our new component just
+        # before that
+        orig_name = xzone_test['CanonicalName']
+        components = orig_name.split('.')
+        if len(components) > 1:
+            components.insert(-1, extension)
+            new_name = '.'.join(components)
+        else:
+            new_name = orig_name + '.' + extension
+
+        xzone_test['CanonicalName'] = new_name
+
+    envvars = [
+        'MallocSecureAllocator=1',
+    ]
+
+    if nano_on_xzone:
+        envvars.append('MallocSecureAllocatorNano=0')
+        envvars.append('MallocNanoOnXzone=1')
+    else:
+        envvars.append('MallocSecureAllocatorNano=1')
+
+    if 'perf' not in xzone_test['Tags'] and \
+            'no_debug' not in xzone_test['Tags'] and \
+            not nano_on_xzone:
+        # This isn't a performance test or otherwise incompatible with
+        # the debug variant of the library, so we can use it for extra
+        # assert coverage.
+        envvars.append('DYLD_IMAGE_SUFFIX=_debug')
+
+    extend_env(xzone_test, envvars)
+
+    # xzone tests aren't eligible for VM testing because
+    # VMs report a single CPU cluster, which xzone malloc
+    # doesn't support
+    new_tags = []
+    for tag in test["Tags"]:
+        if tag == 'VM_PREFERRED':
+            new_tags.append("VM_NOT_PREFERRED")
+        else:
+            new_tags.append(tag)
+
+    xzone_test["Tags"] = new_tags
+
+    return xzone_test
+
+def add_xzone_tests(bats_plist_path, disable_xzone):
+    with open(bats_plist_path, 'rb') as bats_plist_file:
+        orig_bats_plist = plistlib.load(bats_plist_file)
+
+    # Copy all the top-level keys as-is except for the Tests list
+    new_bats_plist = { k: v for k, v in orig_bats_plist.items() if k != 'Tests' }
+
+    tests = []
+    for test in orig_bats_plist['Tests']:
+        disable_pgm(test)
+        # Keep the original test, unless it's xzone-only
+        if 'Tags' not in test or 'xzone_only' not in test['Tags']:
+            test_copy = copy.deepcopy(test)
+            # Explicitly disable xzone malloc, so that the old allocator is
+            # still tested on platforms that have xzone malloc by default
+            envvars = ['MallocSecureAllocator=0']
+            extend_env(test_copy, envvars)
+            tests.append(test_copy)
+
+        if 'Tags' in test and not disable_xzone:
+            if 'xzone' in test['Tags'] or 'xzone_only' in test['Tags']:
+                # This test has been tagged to run with xzone malloc
+                xzone_test = create_xzone_test(test, False)
+                tests.append(xzone_test)
+
+            if 'nano_on_xzone' in test['Tags']:
+                nano_on_xzone_test = create_xzone_test(test, True)
+                tests.append(nano_on_xzone_test)
+
+    new_bats_plist['Tests'] = tests
+
+    with open(bats_plist_path, 'wb') as bats_plist_file:
+        plistlib.dump(new_bats_plist, bats_plist_file, fmt=plistlib.FMT_BINARY)
+
+
+# Note: The env is a list of `key=value`, not a dictionary
+def has_env_var(test, env_var_name):
+    env = test.get('ShellEnv', [])
+    key = env_var_name + '='  # exact match required
+    return any(v.startswith(key) for v in env)
+
+
+def extend_env(test, env_vars):
+    if 'ShellEnv' in test:
+        test['ShellEnv'].extend(env_vars)
+    else:
+        test['ShellEnv'] = env_vars
+
+
+# Disable PGM by setting `MallocProbGuard=0`, but respect existing uses
+def disable_pgm(test):
+    if not has_env_var(test, 'MallocProbGuard'):
+        extend_env(test, ['MallocProbGuard=0'])
+
+
+if __name__ == '__main__':
+    parser = argparse.ArgumentParser(description='Adds xzone malloc tests to BATS plist')
+    parser.add_argument('bats_plist')
+    parser.add_argument('-p', '--platform', help='Platform tests are being run on ()')
+    args = parser.parse_args()
+
+    assert exists(args.bats_plist), 'Expected bats plist as argument'
+
+    disable_xzone_tests = False
+    if args.platform == 'WatchOS':
+        # MallocSecureAllocator=1 is a no-op on arm64_32 (read: all watches),
+        # so don't generate .xzone test variants on watchOS
+        disable_xzone_tests = True
+
+    add_xzone_tests(args.bats_plist, disable_xzone_tests)