From 6608e17a6cdefe09a5869fbf5bf02a369964983c Mon Sep 17 00:00:00 2001
From: Charles Lyding <19598772+clydin@users.noreply.github.com>
Date: Thu, 13 Nov 2025 13:11:55 -0500
Subject: [PATCH] fix(@angular/build): enable test isolation by default in
 browser mode

This commit enables test isolation by default when running tests in a browser.

Disabling test isolation in browser mode has been found to cause non-deterministic test failures. To improve reliability, this change conditionally enables the `isolate` option when a browser provider is active.

Isolation remains disabled for DOM emulation environments to maintain alignment with the traditional Karma/Jasmine experience. Further investigation is needed to determine if isolation can be safely disabled for browser mode in the future.
---
 .../build/src/builders/unit-test/runners/vitest/plugins.ts   | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

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 04554955cd18..7f5bf1a87d85 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
@@ -117,8 +117,9 @@ export async function createVitestConfigPlugin(
         test: {
           setupFiles,
           globals: true,
-          // Default to `false` to align with the Karma/Jasmine experience.
-          isolate: false,
+          // Default to `false` to align with the Karma/Jasmine experience when using DOM emulation
+          // TODO: Investigate how this can be the default for browser mode as well
+          isolate: !!browser?.enabled,
           sequence: { setupFiles: 'list' },
         },
         optimizeDeps: {