fix(@angular/build): ensure TestBed setup is robust in non-isolated Vitest

This commit refines the Angular TestBed initialization within the Vitest runner to ensure correct behavior in non-isolated test environments (`isolate: false`).

Previously, in a non-isolated setup, the TestBed initialization logic in the virtual setup file could be problematic if the file was evaluated multiple times. This could lead to re-registering `beforeEach`/`afterEach` hooks or attempting to re-initialize the TestBed, causing errors or unexpected test behavior.

This change introduces a globally unique symbol guard (`Symbol.for('@angular/cli/testbed-setup')`) that ensures the entire TestBed setup block (including hook registration and `initTestEnvironment`) is executed only once per test run. This prevents redundant executions and potential errors.

Finally, the `isolate` option in Vitest is now explicitly defaulted to `false` when not specified by the user, aligning with the traditional Karma/Jasmine experience.

Author: clydin

packages/angular/build/src/builders/unit-test/runners/vitest/build-options.ts

@@ -49,17 +49,29 @@ function createTestBedInitVirtualFile(
     import { getTestBed, ɵgetCleanupHook as getCleanupHook } from '@angular/core/testing';
     import { BrowserTestingModule, platformBrowserTesting } from '@angular/platform-browser/testing';
     ${providersImport}
-    // Same as https://github.com/angular/angular/blob/05a03d3f975771bb59c7eefd37c01fa127ee2229/packages/core/testing/srcs/test_hooks.ts#L21-L29
-    beforeEach(getCleanupHook(false));
-    afterEach(getCleanupHook(true));
-    @NgModule({
-      providers: [${usesZoneJS ? 'provideZoneChangeDetection(), ' : ''}...providers],
-    })
-    export class TestModule {}
-    getTestBed().initTestEnvironment([BrowserTestingModule, TestModule], platformBrowserTesting(), {
-      errorOnUnknownElements: true,
-      errorOnUnknownProperties: true,
-    });
+
+    const ANGULAR_TESTBED_SETUP = Symbol.for('@angular/cli/testbed-setup');
+    if (!globalThis[ANGULAR_TESTBED_SETUP]) {
+      globalThis[ANGULAR_TESTBED_SETUP] = true;
+
+      // The Angular TestBed needs to be initialized before any tests are run.
+      // In a non-isolated environment, this setup file can be executed multiple times.
+      // The guard condition above ensures that the setup is only performed once.
+
+      // Same as https://github.com/angular/angular/blob/05a03d3f975771bb59c7eefd37c01fa127ee2229/packages/core/testing/srcs/test_hooks.ts#L21-L29
+      beforeEach(getCleanupHook(false));
+      afterEach(getCleanupHook(true));
+
+      @NgModule({
+        providers: [${usesZoneJS ? 'provideZoneChangeDetection(), ' : ''}...providers],
+      })
+      class TestModule {}
+
+      getTestBed().initTestEnvironment([BrowserTestingModule, TestModule], platformBrowserTesting(), {
+        errorOnUnknownElements: true,
+        errorOnUnknownProperties: true,
+      });
+    }
   `;
 }
 

packages/angular/build/src/builders/unit-test/runners/vitest/executor.ts

@@ -223,7 +223,10 @@ export class VitestExecutor implements TestExecutor {
             reporters,
             setupFiles: testSetupFiles,
             projectPlugins,
-            include: [...this.testFileToEntryPoint.keys()],
+            include: [...this.testFileToEntryPoint.keys()].filter(
+              // Filter internal entries
+              (entry) => !entry.startsWith('angular:'),
+            ),
           }),
         ],
       },

packages/angular/build/src/builders/unit-test/runners/vitest/plugins.ts

@@ -125,6 +125,8 @@ export function createVitestConfigPlugin(options: VitestConfigPluginOptions): Vi
           setupFiles: combinedSetupFiles,
           include,
           globals: testConfig?.globals ?? true,
+          // Default to `false` to align with the Karma/Jasmine experience.
+          isolate: testConfig?.isolate ?? false,
           ...(browser ? { browser } : {}),
           // If the user has not specified an environment, use a smart default.
           ...(!testConfig?.environment