diff --git a/packages/SwingSet/test/test-simulate-upgrade.js b/packages/SwingSet/test/test-simulate-upgrade.js
new file mode 100644
index 000000000000..e4c9c1ad4d7a
--- /dev/null
+++ b/packages/SwingSet/test/test-simulate-upgrade.js
@@ -0,0 +1,42 @@
+import { test, simulateIncarnation } from '../tools/prepare-test-env-ava.js';
+
+// eslint-disable-next-line import/order
+import { provideDurableMapStore, vivifyKind } from '@agoric/vat-data';
+
+const initFoo = () => ({ count: 0 });
+const fooBehavior = {
+  increment: ({ state }) => {
+    state.count += 1;
+  },
+  read: ({ state }) => state.count,
+};
+
+test('simulate upgrade', async t => {
+  await simulateIncarnation(async baggage => {
+    // first incarnation
+    const s = provideDurableMapStore(baggage, 'store');
+    const makeFoo = vivifyKind(baggage, 'foo', initFoo, fooBehavior);
+
+    s.init('key1', 'value1');
+
+    const foo1 = makeFoo();
+    s.init('foo1', foo1);
+    foo1.increment();
+    foo1.increment();
+    t.is(foo1.read(), 2);
+  });
+
+  await simulateIncarnation(async baggage => {
+    // second incarnation
+    const s = provideDurableMapStore(baggage, 'store');
+    const makeFoo = vivifyKind(baggage, 'foo', initFoo, fooBehavior);
+
+    t.is(s.get('key1'), 'value1');
+
+    const foo1 = s.get('foo1');
+    t.is(foo1.read(), 2);
+    foo1.increment();
+    t.is(foo1.read(), 3);
+    t.is(makeFoo().read(), 0);
+  });
+});
diff --git a/packages/SwingSet/tools/prepare-test-env-ava.js b/packages/SwingSet/tools/prepare-test-env-ava.js
index 914762bc2453..7465e409d1ed 100644
--- a/packages/SwingSet/tools/prepare-test-env-ava.js
+++ b/packages/SwingSet/tools/prepare-test-env-ava.js
@@ -13,6 +13,8 @@ import '@endo/ses-ava/exported.js';
 import { wrapTest } from '@endo/ses-ava';
 import rawTest from 'ava';
 
+export { simulateIncarnation } from './prepare-test-env.js';
+
 /** @type {typeof rawTest} */
 // eslint-disable-next-line @typescript-eslint/prefer-ts-expect-error
 // @ts-ignore XXX https://github.com/endojs/endo/issues/1235
diff --git a/packages/SwingSet/tools/prepare-test-env.js b/packages/SwingSet/tools/prepare-test-env.js
index 8fa049dd23be..fc80daeead6e 100644
--- a/packages/SwingSet/tools/prepare-test-env.js
+++ b/packages/SwingSet/tools/prepare-test-env.js
@@ -11,39 +11,74 @@ import '@endo/init/pre-bundle-source.js';
 import './install-ses-debug.js';
 import { makeFakeVirtualStuff } from '@agoric/swingset-liveslots/tools/fakeVirtualSupport.js';
 
-const { vom, cm, wpm } = makeFakeVirtualStuff({ cacheSize: 3 });
-
-const {
-  defineKind,
-  defineKindMulti,
-  defineDurableKind,
-  defineDurableKindMulti,
-  makeKindHandle,
-  canBeDurable,
-} = vom;
-
-const {
-  makeScalarBigMapStore,
-  makeScalarBigWeakMapStore,
-  makeScalarBigSetStore,
-  makeScalarBigWeakSetStore,
-} = cm;
-
-const { watchPromise, providePromiseWatcher } = wpm;
-
-const VatData = harden({
-  defineKind,
-  defineKindMulti,
-  defineDurableKind,
-  defineDurableKindMulti,
-  makeKindHandle,
-  providePromiseWatcher,
-  watchPromise,
-  makeScalarBigMapStore,
-  makeScalarBigWeakMapStore,
-  makeScalarBigSetStore,
-  makeScalarBigWeakSetStore,
-  canBeDurable,
-});
+function makeEverything(options) {
+  const { vom, cm, wpm } = makeFakeVirtualStuff(options);
+
+  const {
+    defineKind,
+    defineKindMulti,
+    defineDurableKind,
+    defineDurableKindMulti,
+    makeKindHandle,
+    canBeDurable,
+    flushCache,
+  } = vom;
+
+  const {
+    makeScalarBigMapStore,
+    makeScalarBigWeakMapStore,
+    makeScalarBigSetStore,
+    makeScalarBigWeakSetStore,
+    provideBaggage,
+  } = cm;
+
+  const { watchPromise, providePromiseWatcher } = wpm;
+
+  const vatData = {
+    defineKind,
+    defineKindMulti,
+    defineDurableKind,
+    defineDurableKindMulti,
+    makeKindHandle,
+    providePromiseWatcher,
+    watchPromise,
+    makeScalarBigMapStore,
+    makeScalarBigWeakMapStore,
+    makeScalarBigSetStore,
+    makeScalarBigWeakSetStore,
+    canBeDurable,
+  };
+
+  return harden({ vatData, provideBaggage, flushCache });
+}
+
+// we replace these during simulated upgrade, so each incarnation gets
+// a new set
+let currentVatData = makeEverything({ cacheSize: 3 }).vatData;
+
+// these are exported/imported in pieces, so they are immutable
+const VatData = {};
+for (const name of Object.keys(currentVatData)) {
+  VatData[name] = (...args) => currentVatData[name](...args);
+}
+harden(VatData);
 
 globalThis.VatData = VatData;
+
+let incarnationStore;
+
+// runs async thunk() within a simulated per-upgrade "incarnation"
+export const simulateIncarnation = async thunk => {
+  // make a new backing store by cloning the previous one, if any
+  incarnationStore = new Map(incarnationStore);
+  const { vatData, provideBaggage, flushCache } = makeEverything({
+    cacheSize: 3,
+    fakeStore: incarnationStore,
+  });
+  currentVatData = vatData;
+  const baggage = provideBaggage();
+
+  await thunk(baggage);
+  flushCache();
+};
+harden(simulateIncarnation);
diff --git a/packages/swingset-liveslots/tools/fakeCollectionManager.js b/packages/swingset-liveslots/tools/fakeCollectionManager.js
index 5ea9f44b0b8f..d11954761ab6 100644
--- a/packages/swingset-liveslots/tools/fakeCollectionManager.js
+++ b/packages/swingset-liveslots/tools/fakeCollectionManager.js
@@ -7,6 +7,7 @@ export function makeFakeCollectionManager(vrm, fakeStuff, _options = {}) {
     makeScalarBigSetStore,
     makeScalarBigWeakSetStore,
     initializeStoreKindInfo,
+    provideBaggage,
   } = makeCollectionManager(
     fakeStuff.syscall,
     vrm,
@@ -26,6 +27,7 @@ export function makeFakeCollectionManager(vrm, fakeStuff, _options = {}) {
     makeScalarBigWeakMapStore,
     makeScalarBigSetStore,
     makeScalarBigWeakSetStore,
+    provideBaggage,
   };
 
   const debugTools = {
diff --git a/packages/swingset-liveslots/tools/fakeVirtualSupport.js b/packages/swingset-liveslots/tools/fakeVirtualSupport.js
index e9a551ebaadf..cabedf6a17e2 100644
--- a/packages/swingset-liveslots/tools/fakeVirtualSupport.js
+++ b/packages/swingset-liveslots/tools/fakeVirtualSupport.js
@@ -32,9 +32,9 @@ export function makeFakeLiveSlotsStuff(options = {}) {
     FinalizationRegistry = FakeFinalizationRegistry,
     addToPossiblyDeadSet = () => {},
     addToPossiblyRetiredSet = () => {},
+    fakeStore = new Map(),
   } = options;
 
-  const fakeStore = new Map();
   let sortedKeys;
   let priorKeyReturned;
   let priorKeyIndex;