diff --git a/package.json b/package.json
index e7dd987..41e7b74 100644
--- a/package.json
+++ b/package.json
@@ -13,7 +13,7 @@
     "karma": "cross-env NODE_ENV=test babel-node --plugins=transform-es2015-modules-commonjs ./node_modules/.bin/karma start",
     "babel": "babel src/ --out-dir dist/module",
     "webpack": "babel-node --plugins=transform-es2015-modules-commonjs ./node_modules/.bin/webpack --progress",
-    "test": "npm run format:check && npm run lint && npm run flow-typed && npm run flow && npm run karma",
+    "test": "npm run format:check && npm run lint && npm run flow-typed && npm run flow && npm run vitest && npm run karma",
     "build": "npm run test && npm run babel && npm run webpack",
     "clean": "rimraf dist coverage",
     "reinstall": "rimraf flow-typed && rimraf node_modules && npm install && flow-typed install",
@@ -21,7 +21,8 @@
     "prepare": "husky install",
     "prerelease": "npm run clean && npm run build && git add dist && git commit -m 'ci: check in dist folder' || echo 'Nothing to distribute'",
     "release": "standard-version",
-    "postrelease": "git push && git push --follow-tags && npm publish"
+    "postrelease": "git push && git push --follow-tags && npm publish",
+    "vitest": "vitest"
   },
   "standard-version": {
     "types": [
@@ -86,6 +87,7 @@
   "license": "Apache-2.0",
   "readmeFilename": "README.md",
   "devDependencies": {
+    "@bunchtogether/vite-plugin-flow": "^1.0.2",
     "@commitlint/cli": "^16.2.1",
     "@commitlint/config-conventional": "^16.2.1",
     "@krakenjs/grumbler-scripts": "^8.0.5",
@@ -93,10 +95,13 @@
     "flow-bin": "0.155.0",
     "flow-typed": "^3.8.0",
     "husky": "^7.0.4",
+    "jsdom": "^22.1.0",
     "lint-staged": "^12.4.0",
     "mocha": "^4.1.0",
     "prettier": "^2.6.2",
-    "standard-version": "^9.3.2"
+    "standard-version": "^9.3.2",
+    "vite": "^4.5.0",
+    "vitest": "^0.34.6"
   },
   "dependencies": {
     "@krakenjs/cross-domain-safe-weakmap": "^2.0.2",
diff --git a/src/storage.js b/src/storage.js
index 173fddb..be13481 100644
--- a/src/storage.js
+++ b/src/storage.js
@@ -18,9 +18,13 @@ const DEFAULT_SESSION_STORAGE = 20 * 60 * 1000;
 export function getStorage({
   name,
   lifetime = DEFAULT_SESSION_STORAGE,
+  // a sticky session id helps to identify sdk sessions that were created by other sdks
+  // like the situation where the Braintree SDK loads the PP SDK
+  stickySessionId,
 }: {|
   name: string,
   lifetime?: number,
+  stickySessionId?: string,
 |}): Storage {
   return inlineMemoize(
     getStorage,
@@ -94,7 +98,7 @@ export function getStorage({
 
           if (!session) {
             session = {
-              guid: uniqueID(),
+              guid: stickySessionId || uniqueID(),
               created: now,
             };
           }
diff --git a/src/storage.test.js b/src/storage.test.js
new file mode 100644
index 0000000..2f3b7f2
--- /dev/null
+++ b/src/storage.test.js
@@ -0,0 +1,49 @@
+/* @flow */
+import { vi, describe, test, expect, beforeEach } from "vitest";
+
+import { getStorage } from "./storage";
+import { uniqueID } from "./util";
+
+vi.mock("./util", async () => {
+  const actual = await vi.importActual("./util");
+
+  return {
+    ...actual,
+    uniqueID: vi.fn(() => "unique-id-123"),
+    getGlobal: vi.fn(() => ({})),
+    inlineMemoize: vi.fn((_, impl) => impl()),
+  };
+});
+
+describe("storage", () => {
+  beforeEach(() => {
+    window.localStorage.clear();
+  });
+
+  test("happy path works", () => {
+    // $FlowIssue mock
+    uniqueID.mockReturnValue("fake-id");
+    const { getID } = getStorage({ name: "test" });
+
+    expect(getID()).toEqual("fake-id");
+  });
+
+  test("unique id is used for session id", () => {
+    // $FlowIssue mock
+    uniqueID.mockReturnValue("fake-session-id");
+    const { getSessionID } = getStorage({ name: "test" });
+
+    expect(getSessionID()).toEqual("fake-session-id");
+  });
+
+  test("sticky session id is used for session id", () => {
+    // $FlowIssue mock
+    uniqueID.mockReturnValue("fake-session-id");
+    const { getSessionID } = getStorage({
+      name: "test",
+      stickySessionId: "sticky-session-id",
+    });
+
+    expect(getSessionID()).toEqual("sticky-session-id");
+  });
+});
diff --git a/vite.config.js b/vite.config.js
new file mode 100644
index 0000000..dca910f
--- /dev/null
+++ b/vite.config.js
@@ -0,0 +1,31 @@
+/* eslint-disable eslint-comments/disable-enable-pair */
+/* eslint-disable spaced-comment */
+/* eslint-disable import/no-default-export */
+/// <reference types="vitest" />
+
+// Configure Vitest (https://vitest.dev/config/)
+
+/* @flow */
+
+import { defineConfig } from "vite";
+import { flowPlugin, esbuildFlowPlugin } from "@bunchtogether/vite-plugin-flow";
+
+// $FlowIssue
+export default defineConfig({
+  test: {
+    environment: "jsdom",
+    clearMocks: true,
+    include: ["**/src/**/*.test.js"],
+  },
+  optimizeDeps: {
+    esbuildOptions: {
+      plugins: [esbuildFlowPlugin()],
+    },
+  },
+  plugins: [
+    // $FlowIssue
+    flowPlugin({
+      exclude: "",
+    }),
+  ],
+});