From a3383b14bf67980fb6f45d92ac07a944d37dffd7 Mon Sep 17 00:00:00 2001
From: Charles Lyding <19598772+clydin@users.noreply.github.com>
Date: Fri, 14 Nov 2025 19:32:42 -0500
Subject: [PATCH] fix(@angular/build): disable Vitest test isolation by default

Disables test isolation in Vitest by setting `isolate: false` in the default
Vitest configuration. This change aligns the default test isolation behavior
with the existing Karma/Jasmine experience, promoting standardization across
testing frameworks within the Angular CLI.

This also provides significant performance improvements, especially in browser
mode, by reducing the overhead associated with test isolation. All known issues
related to disabling isolation have been addressed.
---
 .../build/src/builders/unit-test/runners/vitest/plugins.ts     | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/packages/angular/build/src/builders/unit-test/runners/vitest/plugins.ts b/packages/angular/build/src/builders/unit-test/runners/vitest/plugins.ts
index fada9089d84f..538b891e1473 100644
--- a/packages/angular/build/src/builders/unit-test/runners/vitest/plugins.ts
+++ b/packages/angular/build/src/builders/unit-test/runners/vitest/plugins.ts
@@ -117,7 +117,8 @@ export async function createVitestConfigPlugin(
         test: {
           setupFiles,
           globals: true,
-          // Allow Vitest to manage test isolation by its default behavior.
+          // Default to `false` to align with the Karma/Jasmine experience.
+          isolate: false,
           sequence: { setupFiles: 'list' },
         },
         optimizeDeps: {