From b61d1ced3a11fea09e02a95a8b8fbcecbf0944ac Mon Sep 17 00:00:00 2001
From: Kasper Peulen <kasperpeulen@gmail.com>
Date: Wed, 7 Oct 2026 14:34:26 +0200
Subject: [PATCH] fix(browser): wait for setup mocks before importing a test
 file (#11520)

---
 packages/browser/src/client/tester/runner.ts  |  2 ++
 .../mocking-setup-file/browser-setup.ts       |  3 ++
 .../mocking-setup-file/dynamic-import.test.ts |  6 ++++
 .../fixtures/mocking-setup-file/source.ts     |  3 ++
 .../mocking-setup-file/static-import.test.ts  |  6 ++++
 .../mocking-setup-file/vitest.config.ts       | 28 +++++++++++++++++++
 test/browser/specs/mocking.test.ts            | 21 ++++++++++++++
 7 files changed, 69 insertions(+)
 create mode 100644 test/browser/fixtures/mocking-setup-file/browser-setup.ts
 create mode 100644 test/browser/fixtures/mocking-setup-file/dynamic-import.test.ts
 create mode 100644 test/browser/fixtures/mocking-setup-file/source.ts
 create mode 100644 test/browser/fixtures/mocking-setup-file/static-import.test.ts
 create mode 100644 test/browser/fixtures/mocking-setup-file/vitest.config.ts

diff --git a/packages/browser/src/client/tester/runner.ts b/packages/browser/src/client/tester/runner.ts
index e41be5a5b..fef76125f 100644
--- a/packages/browser/src/client/tester/runner.ts
+++ b/packages/browser/src/client/tester/runner.ts
@@ -343,6 +343,8 @@ function createBrowserRunner(
       if (mode === 'collect' && trace !== 'off') {
         await this.commands.triggerCommand('__vitest_startTracing', [])
       }
+      // static imports don't wait for mocks queued by a setup file
+      await mocker.prepare()
       try {
         await import(/* @vite-ignore */ importpath)
       } catch (err) {
diff --git a/test/browser/fixtures/mocking-setup-file/browser-setup.ts b/test/browser/fixtures/mocking-setup-file/browser-setup.ts
new file mode 100644
index 000000000..e518f3911
--- /dev/null
+++ b/test/browser/fixtures/mocking-setup-file/browser-setup.ts
@@ -0,0 +1,3 @@
+import { vi } from 'vitest'
+
+vi.mock('./source', () => ({ answer: () => 'mocked' }))
diff --git a/test/browser/fixtures/mocking-setup-file/dynamic-import.test.ts b/test/browser/fixtures/mocking-setup-file/dynamic-import.test.ts
new file mode 100644
index 000000000..3a281cb6e
--- /dev/null
+++ b/test/browser/fixtures/mocking-setup-file/dynamic-import.test.ts
@@ -0,0 +1,6 @@
+import { expect, test } from 'vitest'
+
+test('a dynamic import gets the mock from the setup file', async () => {
+  const { answer } = await import('./source')
+  expect(answer()).toBe('mocked')
+})
diff --git a/test/browser/fixtures/mocking-setup-file/source.ts b/test/browser/fixtures/mocking-setup-file/source.ts
new file mode 100644
index 000000000..2bb943e67
--- /dev/null
+++ b/test/browser/fixtures/mocking-setup-file/source.ts
@@ -0,0 +1,3 @@
+export function answer() {
+  return 'original'
+}
diff --git a/test/browser/fixtures/mocking-setup-file/static-import.test.ts b/test/browser/fixtures/mocking-setup-file/static-import.test.ts
new file mode 100644
index 000000000..0cd5adc2b
--- /dev/null
+++ b/test/browser/fixtures/mocking-setup-file/static-import.test.ts
@@ -0,0 +1,6 @@
+import { expect, test } from 'vitest'
+import { answer } from './source'
+
+test('a static import gets the mock from the setup file', () => {
+  expect(answer()).toBe('mocked')
+})
diff --git a/test/browser/fixtures/mocking-setup-file/vitest.config.ts b/test/browser/fixtures/mocking-setup-file/vitest.config.ts
new file mode 100644
index 000000000..ac0ac0bd9
--- /dev/null
+++ b/test/browser/fixtures/mocking-setup-file/vitest.config.ts
@@ -0,0 +1,28 @@
+import { fileURLToPath } from 'node:url'
+import { defineConfig } from 'vitest/config'
+import { instances, provider } from '../../settings'
+
+export default defineConfig({
+  cacheDir: fileURLToPath(new URL('./node_modules/.vite', import.meta.url)),
+  plugins: [
+    {
+      // registering the mock takes longer than importing the test file
+      name: 'slow-mock-registration',
+      enforce: 'pre',
+      async resolveId(id, importer) {
+        if (id === './source' && importer?.endsWith('browser-setup.ts')) {
+          await new Promise(resolve => setTimeout(resolve, 500))
+        }
+      },
+    },
+  ],
+  test: {
+    setupFiles: ['./browser-setup.ts'],
+    browser: {
+      enabled: true,
+      provider,
+      instances,
+      headless: true,
+    },
+  },
+})
diff --git a/test/browser/specs/mocking.test.ts b/test/browser/specs/mocking.test.ts
index 62076655a..4c6bbc49c 100644
--- a/test/browser/specs/mocking.test.ts
+++ b/test/browser/specs/mocking.test.ts
@@ -104,3 +104,24 @@ test('mocking out of root', async () => {
     expect(vitest.stdout).toReportPassedTest('basic.test.js', browser)
   })
 })
+
+// fix https://github.com/vitest-dev/vitest/issues/11519
+test('mocks from a setup file apply to static imports of a test file', async () => {
+  const result = await runVitest({
+    root: 'fixtures/mocking-setup-file',
+  })
+
+  onTestFailed(() => {
+    console.error(result.stdout)
+    console.error(result.stderr)
+  })
+
+  expect(result.stderr).toReportNoErrors()
+
+  instances.forEach(({ browser }) => {
+    expect(result.stdout).toReportPassedTest('static-import.test.ts', browser)
+    expect(result.stdout).toReportPassedTest('dynamic-import.test.ts', browser)
+  })
+
+  expect(result.exitCode).toBe(0)
+})
-- 
2.51.2