dev-test: UI events, getComputedStyle and the observers in the browser env

react-tooltip, on hover, called getComputedStyle, MutationObserver and
ResizeObserver, none of which the browser env exposed. The env now
also carries the UI event constructors (MouseEvent, KeyboardEvent,
FocusEvent and the rest), DOMRect, MutationObserver and a bound
getComputedStyle from JSDOM, grouped by kind.

JSDOM has no ResizeObserver. It does no layout either, so no element
ever changes size; the env's ResizeObserver accepts observe() and never
calls back, which is what a real one would do on a page that never
resizes.

packages/dev-test/src/env/browser.spec.ts

@@ -36,6 +36,27 @@ describe('browser', () => {
     expect(document).toBeInstanceOf(Document);
   });
 
+  it('contains the UI event constructors', () => {
+    const div = document.createElement('div');
+
+    expect(() => div.dispatchEvent(new MouseEvent('click'))).not.toThrow();
+    expect(() => div.dispatchEvent(new KeyboardEvent('keydown', { key: 'Enter' }))).not.toThrow();
+    expect(new FocusEvent('focus')).toBeInstanceOf(UIEvent);
+  });
+
+  it('contains getComputedStyle and the observers', () => {
+    const div = document.createElement('div');
+
+    div.style.display = 'none';
+    document.body.appendChild(div);
+
+    expect(getComputedStyle(div).display).toBe('none');
+    expect(() => new MutationObserver(() => undefined).observe(div, { childList: true })).not.toThrow();
+    expect(() => new ResizeObserver(() => undefined).observe(div)).not.toThrow();
+
+    div.remove();
+  });
+
   it('dispatches the global CustomEvent and Event on window', () => {
     expect(() => window.dispatchEvent(new CustomEvent('custom', { detail: 1 }))).not.toThrow();
     expect(() => window.dispatchEvent(new Event('plain'))).not.toThrow();

packages/dev-test/src/env/browser.ts

@@ -1,6 +1,8 @@
 // Copyright 2017-2026 @pezkuwi/dev-test authors & contributors
 // SPDX-License-Identifier: Apache-2.0
 
+import type { DOMWindow } from 'jsdom';
+
 import { JSDOM } from 'jsdom';
 
 /**
@@ -10,6 +12,69 @@ import { JSDOM } from 'jsdom';
  */
 export const BROWSER_OVERRIDES: readonly string[] = ['CustomEvent', 'Event'];
 
+/**
+ * JSDOM does no layout, so no element ever changes size and the callback
+ * never runs. JSDOM has no ResizeObserver of its own.
+ */
+class ResizeObserver {
+  observe (): void {
+    // nothing is ever resized
+  }
+
+  unobserve (): void {
+    // nothing is being watched
+  }
+
+  disconnect (): void {
+    // nothing is being watched
+  }
+}
+
+/** The DOM node hierarchy, which libraries check with instanceof */
+function nodes (window: DOMWindow) {
+  return {
+    CharacterData: window.CharacterData,
+    Comment: window.Comment,
+    Document: window.Document,
+    DocumentFragment: window.DocumentFragment,
+    Element: window.Element,
+    Node: window.Node,
+    NodeList: window.NodeList,
+    SVGElement: window.SVGElement,
+    ShadowRoot: window.ShadowRoot,
+    Text: window.Text
+  };
+}
+
+/** Event constructors. Node has its own Event and CustomEvent, see BROWSER_OVERRIDES */
+function events (window: DOMWindow) {
+  return {
+    CompositionEvent: window.CompositionEvent,
+    CustomEvent: window.CustomEvent,
+    Event: window.Event,
+    FocusEvent: window.FocusEvent,
+    InputEvent: window.InputEvent,
+    KeyboardEvent: window.KeyboardEvent,
+    MouseEvent: window.MouseEvent,
+    TouchEvent: window.TouchEvent,
+    UIEvent: window.UIEvent,
+    WheelEvent: window.WheelEvent
+  };
+}
+
+/** Styles, geometry and the observers */
+function layout (window: DOMWindow) {
+  return {
+    // present on the JSDOM window, absent from its DOMWindow type
+    DOMRect: window['DOMRect'] as typeof DOMRect,
+    DOMRectReadOnly: window['DOMRectReadOnly'] as typeof DOMRectReadOnly,
+    MutationObserver: window.MutationObserver,
+    MutationRecord: window.MutationRecord,
+    ResizeObserver,
+    getComputedStyle: window.getComputedStyle.bind(window)
+  };
+}
+
 /**
  * Export a very basic JSDom environment - this is just enough so we have
  * @testing-environment/react tests passing in this repo
@@ -22,13 +87,9 @@ export function browser () {
   const { window } = new JSDOM('', { url: 'http://localhost' });
 
   return {
-    // The DOM node hierarchy, which libraries check with instanceof, and the
-    // event constructors (Node has its own of these, see BROWSER_OVERRIDES)
-    CustomEvent: window.CustomEvent,
-    Document: window.Document,
-    DocumentFragment: window.DocumentFragment,
-    Element: window.Element,
-    Event: window.Event,
+    ...nodes(window),
+    ...events(window),
+    ...layout(window),
     // All HTML Elements that are defined on the JSDOM window object.
     // (we copied as-is from the types definition). We cannot get this
     // via Object.keys(window).filter(...) so we have to specify explicitly
@@ -103,11 +164,6 @@ export function browser () {
     HTMLUListElement: window.HTMLUListElement,
     HTMLUnknownElement: window.HTMLUnknownElement,
     HTMLVideoElement: window.HTMLVideoElement,
-    // the rest of the node hierarchy
-    Node: window.Node,
-    SVGElement: window.SVGElement,
-    ShadowRoot: window.ShadowRoot,
-    Text: window.Text,
     // normal service resumes, the base top-level names
     crypto: window.crypto,
     document: window.document,