diff --git a/static_src/shared/dom-helpers.test.js b/static_src/shared/dom-helpers.test.js
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+++ b/static_src/shared/dom-helpers.test.js
@@ -0,0 +1,100 @@
+// Copyright 2019 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import {assert} from 'chai';
+import {isTextInput, findDeepEventTarget} from './dom-helpers.js';
+
+describe('isTextInput', () => {
+  it('returns true for select', () => {
+    const element = document.createElement('select');
+    assert.isTrue(isTextInput(element));
+  });
+
+  it('returns true for input tags that take text input', () => {
+    const element = document.createElement('input');
+    assert.isTrue(isTextInput(element));
+
+    element.type = 'text';
+    assert.isTrue(isTextInput(element));
+
+    element.type = 'password';
+    assert.isTrue(isTextInput(element));
+
+    element.type = 'number';
+    assert.isTrue(isTextInput(element));
+
+    element.type = 'date';
+    assert.isTrue(isTextInput(element));
+  });
+
+  it('returns false for input tags without text input', () => {
+    const element = document.createElement('input');
+
+    element.type = 'button';
+    assert.isFalse(isTextInput(element));
+
+    element.type = 'submit';
+    assert.isFalse(isTextInput(element));
+
+    element.type = 'checkbox';
+    assert.isFalse(isTextInput(element));
+
+    element.type = 'radio';
+    assert.isFalse(isTextInput(element));
+  });
+
+  it('returns true for textarea', () => {
+    const element = document.createElement('textarea');
+    assert.isTrue(isTextInput(element));
+  });
+
+  it('returns true for contenteditable', () => {
+    const element = document.createElement('div');
+    element.contentEditable = 'true';
+    assert.isTrue(isTextInput(element));
+
+    element.contentEditable = 'false';
+    assert.isFalse(isTextInput(element));
+  });
+
+  it('returns false for non-input', () => {
+    assert.isFalse(isTextInput(document.createElement('div')));
+    assert.isFalse(isTextInput(document.createElement('table')));
+    assert.isFalse(isTextInput(document.createElement('tr')));
+    assert.isFalse(isTextInput(document.createElement('td')));
+    assert.isFalse(isTextInput(document.createElement('href')));
+    assert.isFalse(isTextInput(document.createElement('random-elment')));
+    assert.isFalse(isTextInput(document.createElement('p')));
+  });
+});
+
+describe('findDeepEventTarget', () => {
+  it('returns empty for event without target', () => {
+    const event = new Event('whatsup');
+    assert.isUndefined(findDeepEventTarget(event));
+  });
+
+  it('returns target for event with target', (done) => {
+    const element = document.createElement('div');
+    element.addEventListener('hello', (e) => {
+      assert.deepEqual(findDeepEventTarget(e), element);
+      done();
+    });
+    element.dispatchEvent(new Event('hello'));
+  });
+
+  it('returns target for event coming from shadowRoot', (done) => {
+    const target = document.createElement('button');
+    const parent = document.createElement('div');
+    parent.appendChild(target);
+    parent.attachShadow({mode: 'open'});
+
+    parent.addEventListener('shadow-root', (e) => {
+      assert.deepEqual(findDeepEventTarget(e), target);
+      done();
+    });
+
+    target.dispatchEvent(new Event('shadow-root', {bubbles: true}));
+  });
+});