diff --git a/a3p-integration/proposals/a:vaults-auctions/saveAuctionInstance.js b/a3p-integration/proposals/a:vaults-auctions/saveAuctionInstance.js
index a5b8e921d81f..23d2e59f3af0 100755
--- a/a3p-integration/proposals/a:vaults-auctions/saveAuctionInstance.js
+++ b/a3p-integration/proposals/a:vaults-auctions/saveAuctionInstance.js
@@ -1,16 +1,3 @@
-#!/usr/bin/env node
-/* eslint-env node */
-import { writeFile } from 'fs/promises';
-import { getInstanceBoardId } from '@agoric/synthetic-chain';
-import assert from 'node:assert/strict';
+import { recordAuctioneerInstance } from './vatDetails.js';
 
-const { env } = process;
-
-const oldAuctionInstance = await getInstanceBoardId('auctioneer');
-assert(oldAuctionInstance, 'no auction instance found');
-console.log('old auction instance ', oldAuctionInstance, env.HOME);
-
-await writeFile(
-  `${env.HOME}/.agoric/previousInstance.json`,
-  oldAuctionInstance,
-);
+await recordAuctioneerInstance();
diff --git a/a3p-integration/proposals/a:vaults-auctions/upgradeVaults.test.js b/a3p-integration/proposals/a:vaults-auctions/upgradeVaults.test.js
index 7f50368d3a43..cc0655cc0143 100644
--- a/a3p-integration/proposals/a:vaults-auctions/upgradeVaults.test.js
+++ b/a3p-integration/proposals/a:vaults-auctions/upgradeVaults.test.js
@@ -16,10 +16,11 @@ import {
   pushPrices,
   USER1ADDR,
 } from '@agoric/synthetic-chain';
-import { readFile } from 'node:fs/promises';
-import { getDetailsMatchingVats } from './vatDetails.js';
-
-const { env } = process;
+import { readFile, rm } from 'node:fs/promises';
+import {
+  getDetailsMatchingVats,
+  lastAuctionInstancePathname,
+} from './vatDetails.js';
 
 const oraclesByBrand = new Map();
 
@@ -106,11 +107,9 @@ const verifyVaultPriceUpdate = async t => {
 };
 
 const verifyAuctionInstance = async t => {
-  const newAuctionInstance = await getInstanceBoardId('auctioneer');
-  const oldInstance = await readFile(
-    `${env.HOME}/.agoric/previousInstance.json`,
-    'utf-8',
-  );
+  const newAuctionInstance = getInstanceBoardId('auctioneer');
+  const oldInstance = await readFile(lastAuctionInstancePathname, 'utf-8');
+  await rm(lastAuctionInstancePathname);
 
   console.log(
     `new: ${newAuctionInstance} should be different from ${oldInstance}`,
diff --git a/a3p-integration/proposals/a:vaults-auctions/vatDetails.js b/a3p-integration/proposals/a:vaults-auctions/vatDetails.js
index 2cd4c2c949db..c7b545a26d5f 100644
--- a/a3p-integration/proposals/a:vaults-auctions/vatDetails.js
+++ b/a3p-integration/proposals/a:vaults-auctions/vatDetails.js
@@ -1,4 +1,10 @@
+/* eslint-env node */
+import { getInstanceBoardId } from '@agoric/synthetic-chain';
 import dbOpenAmbient from 'better-sqlite3';
+import { writeFile } from 'fs/promises';
+import assert from 'node:assert/strict';
+
+const { env } = process;
 
 const HOME = process.env.HOME;
 
@@ -99,3 +105,13 @@ export const getDetailsMatchingVats = async vatName => {
 
   return infos;
 };
+
+export const lastAuctionInstancePathname = `${env.HOME}/.agoric/lastAuctioneerInstance.json`;
+
+export const recordAuctioneerInstance = async () => {
+  const oldAuctionInstance = getInstanceBoardId('auctioneer');
+  assert(oldAuctionInstance, 'no auction instance found');
+  console.log('old auction instance ', oldAuctionInstance, env.HOME);
+
+  await writeFile(lastAuctionInstancePathname, oldAuctionInstance);
+};