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diff --git a/mfbt/tests/TestNonDereferenceable.cpp b/mfbt/tests/TestNonDereferenceable.cpp
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+++ b/mfbt/tests/TestNonDereferenceable.cpp
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include <utility>
+
+#include "mozilla/Assertions.h"
+#include "mozilla/NonDereferenceable.h"
+
+using mozilla::NonDereferenceable;
+
+#define CHECK MOZ_RELEASE_ASSERT
+
+void TestNonDereferenceableSimple() {
+  // Default construction.
+  NonDereferenceable<int> nd0;
+  CHECK(!nd0);
+  CHECK(!nd0.value());
+
+  int i = 1;
+  int i2 = 2;
+
+  // Construction with pointer.
+  NonDereferenceable<int> nd1(&i);
+  CHECK(!!nd1);
+  CHECK(nd1.value() == reinterpret_cast<uintptr_t>(&i));
+
+  // Assignment with pointer.
+  nd1 = &i2;
+  CHECK(nd1.value() == reinterpret_cast<uintptr_t>(&i2));
+
+  // Copy-construction.
+  NonDereferenceable<int> nd2(nd1);
+  CHECK(nd2.value() == reinterpret_cast<uintptr_t>(&i2));
+
+  // Copy-assignment.
+  nd2 = nd0;
+  CHECK(!nd2.value());
+
+  // Move-construction.
+  NonDereferenceable<int> nd3{NonDereferenceable<int>(&i)};
+  CHECK(nd3.value() == reinterpret_cast<uintptr_t>(&i));
+
+  // Move-assignment.
+  nd3 = std::move(nd1);
+  CHECK(nd3.value() == reinterpret_cast<uintptr_t>(&i2));
+  // Note: Not testing nd1's value because we don't want to assume what state
+  // it is left in after move. But at least it should be reusable:
+  nd1 = &i;
+  CHECK(nd1.value() == reinterpret_cast<uintptr_t>(&i));
+}
+
+void TestNonDereferenceableHierarchy() {
+  struct Base1 {
+    // Member variable, to make sure Base1 is not empty.
+    int x1;
+  };
+  struct Base2 {
+    int x2;
+  };
+  struct Derived : Base1, Base2 {};
+
+  Derived d;
+
+  // Construct NonDereferenceable from raw pointer.
+  NonDereferenceable<Derived> ndd = NonDereferenceable<Derived>(&d);
+  CHECK(ndd);
+  CHECK(ndd.value() == reinterpret_cast<uintptr_t>(&d));
+
+  // Cast Derived to Base1.
+  NonDereferenceable<Base1> ndb1 = ndd;
+  CHECK(ndb1);
+  CHECK(ndb1.value() == reinterpret_cast<uintptr_t>(static_cast<Base1*>(&d)));
+
+  // Cast Base1 back to Derived.
+  NonDereferenceable<Derived> nddb1 = ndb1;
+  CHECK(nddb1.value() == reinterpret_cast<uintptr_t>(&d));
+
+  // Cast Derived to Base2.
+  NonDereferenceable<Base2> ndb2 = ndd;
+  CHECK(ndb2);
+  CHECK(ndb2.value() == reinterpret_cast<uintptr_t>(static_cast<Base2*>(&d)));
+  // Sanity check that Base2 should be offset from the start of Derived.
+  CHECK(ndb2.value() != ndd.value());
+
+  // Cast Base2 back to Derived.
+  NonDereferenceable<Derived> nddb2 = ndb2;
+  CHECK(nddb2.value() == reinterpret_cast<uintptr_t>(&d));
+
+  // Note that it's not possible to jump between bases, as they're not obviously
+  // related, i.e.: `NonDereferenceable<Base2> ndb22 = ndb1;` doesn't compile.
+  // However it's possible to explicitly navigate through the derived object:
+  NonDereferenceable<Base2> ndb22 = NonDereferenceable<Derived>(ndb1);
+  CHECK(ndb22.value() == reinterpret_cast<uintptr_t>(static_cast<Base2*>(&d)));
+
+  // Handling nullptr; should stay nullptr even for offset bases.
+  ndd = nullptr;
+  CHECK(!ndd);
+  CHECK(!ndd.value());
+  ndb1 = ndd;
+  CHECK(!ndb1);
+  CHECK(!ndb1.value());
+  ndb2 = ndd;
+  CHECK(!ndb2);
+  CHECK(!ndb2.value());
+  nddb2 = ndb2;
+  CHECK(!nddb2);
+  CHECK(!nddb2.value());
+}
+
+template <typename T, size_t Index>
+struct CRTPBase {
+  // Convert `this` from `CRTPBase*` to `T*` while construction is still in
+  // progress; normally UBSan -fsanitize=vptr would catch this, but using
+  // NonDereferenceable should keep UBSan happy.
+  CRTPBase() : mDerived(this) {}
+  NonDereferenceable<T> mDerived;
+};
+
+void TestNonDereferenceableCRTP() {
+  struct Derived : CRTPBase<Derived, 1>, CRTPBase<Derived, 2> {};
+  using Base1 = Derived::CRTPBase<Derived, 1>;
+  using Base2 = Derived::CRTPBase<Derived, 2>;
+
+  Derived d;
+  // Verify that base constructors have correctly captured the address of the
+  // (at the time still incomplete) derived object.
+  CHECK(d.Base1::mDerived.value() == reinterpret_cast<uintptr_t>(&d));
+  CHECK(d.Base2::mDerived.value() == reinterpret_cast<uintptr_t>(&d));
+
+  // Construct NonDereferenceable from raw pointer.
+  NonDereferenceable<Derived> ndd = NonDereferenceable<Derived>(&d);
+  CHECK(ndd);
+  CHECK(ndd.value() == reinterpret_cast<uintptr_t>(&d));
+
+  // Cast Derived to Base1.
+  NonDereferenceable<Base1> ndb1 = ndd;
+  CHECK(ndb1);
+  CHECK(ndb1.value() == reinterpret_cast<uintptr_t>(static_cast<Base1*>(&d)));
+
+  // Cast Base1 back to Derived.
+  NonDereferenceable<Derived> nddb1 = ndb1;
+  CHECK(nddb1.value() == reinterpret_cast<uintptr_t>(&d));
+
+  // Cast Derived to Base2.
+  NonDereferenceable<Base2> ndb2 = ndd;
+  CHECK(ndb2);
+  CHECK(ndb2.value() == reinterpret_cast<uintptr_t>(static_cast<Base2*>(&d)));
+  // Sanity check that Base2 should be offset from the start of Derived.
+  CHECK(ndb2.value() != ndd.value());
+
+  // Cast Base2 back to Derived.
+  NonDereferenceable<Derived> nddb2 = ndb2;
+  CHECK(nddb2.value() == reinterpret_cast<uintptr_t>(&d));
+
+  // Note that it's not possible to jump between bases, as they're not obviously
+  // related, i.e.: `NonDereferenceable<Base2> ndb22 = ndb1;` doesn't compile.
+  // However it's possible to explicitly navigate through the derived object:
+  NonDereferenceable<Base2> ndb22 = NonDereferenceable<Derived>(ndb1);
+  CHECK(ndb22.value() == reinterpret_cast<uintptr_t>(static_cast<Base2*>(&d)));
+}
+
+int main() {
+  TestNonDereferenceableSimple();
+  TestNonDereferenceableHierarchy();
+  TestNonDereferenceableCRTP();
+
+  return 0;
+}