Restore setTimeout fallback, clean up test helpers

- Restore setTimeout fallback in tasks.ts for environments without
  queueMicrotask or MutationObserver
- Remove unused Assertion import in knockout test helper
- Remove redundant assert.isNotNull before null throw guard

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: 2 people

builds/knockout/helpers/mocha-test-helpers.js

@@ -1,6 +1,4 @@
 ;(function (global) {
-  const Assertion = chai.Assertion
-
   function restoreAfter(cleanups, object, propertyName) {
     const originalValue = object[propertyName]
     cleanups.push(function () {
@@ -53,7 +51,7 @@
 
   function expectEqualOneOf(actual, expectedPossibilities) {
     const matches = expectedPossibilities.some(function (expected) { return chai.util.eql(actual, expected) })
-    new Assertion(matches, 'expected value to deeply equal one of the provided possibilities').to.equal(true)
+    expect(matches, 'expected value to deeply equal one of the provided possibilities').to.equal(true)
   }
 
   function expectContainHtml(actual, expectedHtml, postProcessCleanedHtml) {

packages/utils/helpers/mocha-test-helpers.ts

@@ -39,7 +39,6 @@ export function nodeText(node: Node) {
 type HtmlNode = Node & { innerHTML: string }
 
 function assertHtmlNode(node: Node | null): asserts node is HtmlNode {
-  assert.isNotNull(node, 'expected node to exist')
   if (node === null) {
     throw new Error('expected node to exist')
   }

packages/utils/src/tasks.ts

@@ -38,6 +38,8 @@ if (schedulerGlobal && typeof schedulerGlobal.queueMicrotask === 'function') {
       div.setAttribute('data-task-scheduler', toggle ? '1' : '0')
     }
   })()
+} else {
+  options.taskScheduler = callback => setTimeout(callback, 0)
 }
 
 function processTasks() {