diff --git a/extension/tests/human-popup.test.mjs b/extension/tests/human-popup.test.mjs
new file mode 100644
index 0000000..10e13c4
--- /dev/null
+++ b/extension/tests/human-popup.test.mjs
@@ -0,0 +1,43 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import {readFile} from 'node:fs/promises';
+import {captureAccount, fillAccount} from '../human-api.mjs';
+
+test('popup is only the human vault v0 surface', async () => {
+  const html = await readFile(new URL('../popup.html', import.meta.url), 'utf8');
+  assert.match(html, /My vault/);
+  assert.match(html, /Save autofilled login/);
+  assert.match(html, /browser autofill this site's login/);
+  assert.match(html, /Lock vault/);
+  assert.match(html, /Settings/);
+  assert.doesNotMatch(html, /id="juice-panel"/);
+  assert.doesNotMatch(html, /id="human-username"/);
+  assert.doesNotMatch(html, /id="human-password"/);
+  assert.doesNotMatch(html, /<iframe/);
+  assert.ok(!html.includes('src="popup.mjs"'));
+});
+
+test('capture and fill require one clear filled same-origin login form', () => {
+  const old = {location:globalThis.location,document:globalThis.document,window:globalThis.window,HTMLInputElement:globalThis.HTMLInputElement,Event:globalThis.Event};
+  const makeInput = (type,value) => ({
+    type,value,disabled:false,readOnly:false,form:null,
+    getClientRects:()=>[{}],dispatchEvent(){}
+  });
+  const user=makeInput('email','person@example.com'), password=makeInput('password','secret');
+  const form={action:'https://example.com/login',querySelectorAll:()=>[user,password]};
+  user.form=form;password.form=form;
+  globalThis.location={protocol:'https:',origin:'https://example.com',href:'https://example.com/login'};
+  globalThis.window={top:null};globalThis.window.top=globalThis.window;
+  globalThis.document={querySelectorAll:selector=>selector==='input[type="password"]'?[password]:[user,password]};
+  globalThis.HTMLInputElement=function(){};
+  globalThis.HTMLInputElement.prototype={};
+  Object.defineProperty(globalThis.HTMLInputElement.prototype,'value',{set(v){this._set=v},configurable:true});
+  globalThis.Event=class { constructor(type,opts){this.type=type;this.opts=opts} };
+  try {
+    assert.deepEqual(captureAccount('https://example.com'),{username:'person@example.com',password:'secret'});
+    assert.equal(captureAccount('https://other.example'),null);
+    assert.equal(fillAccount('https://example.com',{username:'u',password:'p'}),true);
+  } finally {
+    Object.assign(globalThis,old);
+  }
+});