diff --git a/package-lock.json b/package-lock.json
index 375e66e..60659ad 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -77,6 +77,7 @@
         "eslint-plugin-prettier": "^5.5.4",
         "eslint-plugin-react-hooks": "^5.1.0",
         "eslint-plugin-react-refresh": "^0.4.16",
+        "fake-indexeddb": "^6.2.5",
         "globals": "^15.14.0",
         "postcss": "^8.4.49",
         "prettier": "^3.7.4",
@@ -5966,6 +5967,16 @@
       "integrity": "sha512-fjquC59cD7CyW6urNXK0FBufkZcoiGG80wTuPujX590cB5Ttln20E2UB4S/WARVqhXffZl2LNgS+gQdPIIim/g==",
       "license": "MIT"
     },
+    "node_modules/fake-indexeddb": {
+      "version": "6.2.5",
+      "resolved": "https://registry.npmjs.org/fake-indexeddb/-/fake-indexeddb-6.2.5.tgz",
+      "integrity": "sha512-CGnyrvbhPlWYMngksqrSSUT1BAVP49dZocrHuK0SvtR0D5TMs5wP0o3j7jexDJW01KSadjBp1M/71o/KR3nD1w==",
+      "dev": true,
+      "license": "Apache-2.0",
+      "engines": {
+        "node": ">=18"
+      }
+    },
     "node_modules/fast-deep-equal": {
       "version": "3.1.3",
       "resolved": "https://registry.npmjs.org/fast-deep-equal/-/fast-deep-equal-3.1.3.tgz",
diff --git a/package.json b/package.json
index f69413a..4d776be 100644
--- a/package.json
+++ b/package.json
@@ -85,6 +85,7 @@
     "eslint-plugin-prettier": "^5.5.4",
     "eslint-plugin-react-hooks": "^5.1.0",
     "eslint-plugin-react-refresh": "^0.4.16",
+    "fake-indexeddb": "^6.2.5",
     "globals": "^15.14.0",
     "postcss": "^8.4.49",
     "prettier": "^3.7.4",
diff --git a/src/services/relay-selection.test.ts b/src/services/relay-selection.test.ts
index 2dc8a63..fca0201 100644
--- a/src/services/relay-selection.test.ts
+++ b/src/services/relay-selection.test.ts
@@ -6,12 +6,15 @@ import { describe, it, expect, beforeEach } from "vitest";
 import { selectRelaysForFilter } from "./relay-selection";
 import { EventStore } from "applesauce-core";
 import type { NostrEvent } from "nostr-tools";
+import relayListCache from "./relay-list-cache";
 
 describe("selectRelaysForFilter", () => {
   let eventStore: EventStore;
 
-  beforeEach(() => {
+  beforeEach(async () => {
     eventStore = new EventStore();
+    // Clear the relay list cache to ensure test isolation
+    await relayListCache.clear();
   });
 
   describe("fallback behavior", () => {
diff --git a/src/test/setup.ts b/src/test/setup.ts
new file mode 100644
index 0000000..eba54c2
--- /dev/null
+++ b/src/test/setup.ts
@@ -0,0 +1,7 @@
+/**
+ * Vitest setup file
+ *
+ * Polyfills IndexedDB for Node.js test environment.
+ * This allows Dexie to work in tests without a browser.
+ */
+import "fake-indexeddb/auto";
diff --git a/vitest.config.ts b/vitest.config.ts
index 2b29d01..3674afd 100644
--- a/vitest.config.ts
+++ b/vitest.config.ts
@@ -5,6 +5,7 @@ export default defineConfig({
   test: {
     globals: true,
     environment: "node",
+    setupFiles: ["./src/test/setup.ts"],
   },
   resolve: {
     alias: {