--- /dev/null
+++ libmalloc/libmalloc-374.100.5/tests/malloc_zone_unregister_test.c
@@ -0,0 +1,67 @@
+//
+//  malloc_zone_unregister_test.c
+//  libmalloc
+//
+//  Tests for malloc_zone_unregister().
+//
+
+#include <darwintest.h>
+
+#include <malloc_private.h>
+#include <malloc/malloc.h>
+#include <stdlib.h>
+
+T_GLOBAL_META(T_META_RUN_CONCURRENTLY(true));
+
+extern int32_t malloc_num_zones;
+extern malloc_zone_t **malloc_zones;
+
+T_DECL(malloc_zone_unregister_establish_custom_default_zone,
+		"Unregister all initial zones and register a custom default zone",
+		T_META_ENVVAR("MallocNanoZone=1"))
+{
+  void *ptr = malloc(7);
+  T_EXPECT_NOTNULL(malloc_zone_from_ptr(ptr), "can find zone for allocation");
+  T_EXPECT_TRUE(malloc_claimed_address(ptr), "ptr is claimed");
+
+  T_ASSERT_LE(malloc_num_zones, 10, "at most 10 initial zones");
+  malloc_zone_t *initial_zones[10];
+  uint32_t initial_zone_count = malloc_num_zones;
+
+  // Unregister initial zones
+  for (uint32_t i = 0; i < initial_zone_count; i++) {
+    initial_zones[i] = malloc_zones[0];
+    malloc_zone_unregister(malloc_zones[0]);
+  }
+  T_EXPECT_EQ(malloc_num_zones, 0, "unregistered initial zones");
+
+  // No zones, no results, no crash
+  T_EXPECT_NULL(malloc_zone_from_ptr(ptr), "cannot find zone");
+  T_EXPECT_FALSE(malloc_claimed_address(ptr), "ptr not claimed");
+
+  // Create and register custom default zone
+  malloc_zone_t *custom_zone = malloc_create_zone(0, 0);
+
+  // Custom default zone only, no results, no crash
+  T_EXPECT_NULL(malloc_zone_from_ptr(ptr), "cannot find zone");
+  T_EXPECT_FALSE(malloc_claimed_address(ptr), "ptr not claimed");
+
+  // Re-register initial zones
+  for (uint32_t i = 0; i < initial_zone_count; i++) {
+    malloc_zone_register(initial_zones[i]);
+  }
+  T_EXPECT_EQ(malloc_num_zones, initial_zone_count + 1, "re-registered initial zones");
+
+  // Custom default zone plus initial zones
+  T_EXPECT_NOTNULL(malloc_zone_from_ptr(ptr), "can find zone for allocation");
+  T_EXPECT_TRUE(malloc_claimed_address(ptr), "ptr is claimed");
+
+  // Check that the custom zone is the default zone
+  void *ptr2 = malloc(7);
+  T_EXPECT_EQ(malloc_zones[0], custom_zone, "custom zone is zone 0");
+  T_EXPECT_EQ(malloc_zone_from_ptr(ptr2), malloc_default_zone(), "we lookup the virtual zone for the custom zone");
+  T_EXPECT_TRUE(malloc_zone_claimed_address(custom_zone, ptr2), "custom zone claims ptr");
+
+  free(ptr2);
+  free(ptr);
+}