fix(browser): don't fail when calling vi.useFakeTimers (#4992)

packages/vitest/src/integrations/mock/timers.ts

@@ -138,10 +138,20 @@ export class FakeTimers {
       if (this._userConfig?.toFake?.includes('nextTick') && isChildProcess())
         throw new Error('process.nextTick cannot be mocked inside child_process')
 
+      const existingFakedMethods = (this._userConfig?.toFake || toFake).filter((method) => {
+        switch (method) {
+          case 'hrtime':
+          case 'nextTick':
+            return typeof process !== 'undefined' && method in process && process[method]
+          default:
+            return method in globalThis && globalThis[method]
+        }
+      })
+
       this._clock = this._fakeTimers.install({
         now: Date.now(),
-        toFake,
         ...this._userConfig,
+        toFake: existingFakedMethods,
       })
 
       this._fakingTime = true

packages/vitest/src/utils/base.ts

@@ -151,7 +151,7 @@ class AggregateErrorPonyfill extends Error {
 export { AggregateErrorPonyfill as AggregateError }
 
 export function isChildProcess(): boolean {
-  return !!process?.send
+  return typeof process !== 'undefined' && !!process.send
 }
 
 export function setProcessTitle(title: string) {

test/browser/specs/runner.test.mjs

@@ -11,8 +11,8 @@ const {
 } = await runVitest()
 
 await test('tests are actually running', async () => {
-  assert.ok(browserResultJson.testResults.length === 11, 'Not all the tests have been run')
-  assert.ok(passedTests.length === 9, 'Some tests failed')
+  assert.ok(browserResultJson.testResults.length === 12, 'Not all the tests have been run')
+  assert.ok(passedTests.length === 10, 'Some tests failed')
   assert.ok(failedTests.length === 2, 'Some tests have passed but should fail')
 
   assert.doesNotMatch(stderr, /Unhandled Error/, 'doesn\'t have any unhandled errors')

test/browser/test/timers.test.ts

@@ -0,0 +1,19 @@
+import { afterEach, expect, it, vi } from 'vitest'
+
+afterEach(() => {
+  vi.useRealTimers()
+})
+
+it('only runs a setTimeout callback once (ever)', () => {
+  vi.useFakeTimers()
+
+  const fn = vi.fn()
+  setTimeout(fn, 0)
+  expect(fn).toHaveBeenCalledTimes(0)
+
+  vi.runAllTimers()
+  expect(fn).toHaveBeenCalledTimes(1)
+
+  vi.runAllTimers()
+  expect(fn).toHaveBeenCalledTimes(1)
+})