diff --git a/tests/nostr/defaultClient.test.mjs b/tests/nostr/defaultClient.test.mjs
new file mode 100644
index 00000000..ae752adb
--- /dev/null
+++ b/tests/nostr/defaultClient.test.mjs
@@ -0,0 +1,72 @@
+import { describe, it, after } from "node:test";
+import assert from "node:assert/strict";
+import "../test-setup.mjs";
+
+// Mock dependencies before importing the module under test
+if (!globalThis.WebSocket) {
+  globalThis.WebSocket = class MockWebSocket {
+    send() {}
+    close() {}
+  };
+}
+
+if (!globalThis.localStorage) {
+  globalThis.localStorage = {
+    getItem: () => null,
+    setItem: () => {},
+    removeItem: () => {},
+    clear: () => {},
+  };
+}
+
+// Set dev mode override
+globalThis.__BITVID_DEV_MODE_OVERRIDE__ = true;
+
+// Mock console to suppress logs during tests
+const originalConsole = { ...console };
+globalThis.console = {
+  ...console,
+  log: () => {},
+  info: () => {},
+  warn: () => {},
+  error: () => {},
+  debug: () => {},
+};
+
+// Import modules dynamically after setting up mocks
+const { nostrClient } = await import("../../js/nostr/defaultClient.js");
+const { DEFAULT_RELAY_URLS } = await import("../../js/nostr/toolkit.js");
+const { getRegisteredNostrClient } = await import("../../js/nostrClientRegistry.js");
+const { NostrClient } = await import("../../js/nostr/client.js");
+
+describe("Default NostrClient", () => {
+  after(() => {
+    // Restore console
+    globalThis.console = originalConsole;
+    // Clean up globals if desired, though process isolation makes this optional
+    delete globalThis.__BITVID_DEV_MODE_OVERRIDE__;
+  });
+  it("should be an instance of NostrClient", () => {
+    assert.ok(nostrClient instanceof NostrClient);
+  });
+
+  it("should be configured with default relays", () => {
+    const expectedRelays = Array.from(DEFAULT_RELAY_URLS);
+    assert.deepEqual(nostrClient.relays, expectedRelays);
+  });
+
+  it("should be initialized with default read relays", () => {
+    const expectedRelays = Array.from(DEFAULT_RELAY_URLS);
+    assert.deepEqual(nostrClient.readRelays, expectedRelays);
+  });
+
+  it("should be initialized with default write relays", () => {
+    const expectedRelays = Array.from(DEFAULT_RELAY_URLS);
+    assert.deepEqual(nostrClient.writeRelays, expectedRelays);
+  });
+
+  it("should be registered as the default client", () => {
+    const registered = getRegisteredNostrClient();
+    assert.strictEqual(registered, nostrClient);
+  });
+});