fix(@angular/build): use virtual module for Karma TestBed initialization

Using a virtual module for the Karma-based unit testing setup allows for
the Angular packages used within the TestBed initialization to resolve to
the same dependencies used within the application and test code. This avoids
the potential for multiple copies of `@angular/core` within the test output
which can result in TestBed execution failure due to the module level variable
usage within TestBed.

Author: clydin

packages/angular/build/src/builders/karma/application_builder.ts

@@ -17,6 +17,7 @@ import { ReadableStreamController } from 'node:stream/web';
 import { globSync } from 'tinyglobby';
 import { BuildOutputFileType } from '../../tools/esbuild/bundler-context';
 import { emitFilesToDisk } from '../../tools/esbuild/utils';
+import { createVirtualModulePlugin } from '../../tools/esbuild/virtual-module-plugin';
 import { buildApplicationInternal } from '../application/index';
 import { ApplicationBuilderInternalOptions } from '../application/options';
 import { Result, ResultFile, ResultKind } from '../application/results';
@@ -383,7 +384,7 @@ async function initializeApplication(
   if (options.main) {
     entryPoints.set(mainName, options.main);
   } else {
-    entryPoints.set(mainName, localResolve('./polyfills/init_test_bed.js'));
+    entryPoints.set(mainName, 'angular:test-bed-init');
   }
 
   const instrumentForCoverage = options.codeCoverage
@@ -429,9 +430,30 @@ async function initializeApplication(
     externalDependencies: options.externalDependencies,
   };
 
+  const virtualTestBedInit = createVirtualModulePlugin({
+    namespace: 'angular:test-bed-init',
+    loadContent: async () => {
+      const contents: string[] = [
+        // Initialize the Angular testing environment
+        `import { getTestBed } from '@angular/core/testing';`,
+        `import { BrowserTestingModule, platformBrowserTesting } from '@angular/platform-browser/testing';`,
+        `getTestBed().initTestEnvironment(BrowserTestingModule, platformBrowserTesting(), {`,
+        `  errorOnUnknownElements: true,`,
+        `  errorOnUnknownProperties: true,`,
+        '});',
+      ];
+
+      return {
+        contents: contents.join('\n'),
+        loader: 'js',
+        resolveDir: projectSourceRoot,
+      };
+    },
+  });
+
   // Build tests with `application` builder, using test files as entry points.
   const [buildOutput, buildIterator] = await first(
-    buildApplicationInternal(buildOptions, context),
+    buildApplicationInternal(buildOptions, context, { codePlugins: [virtualTestBedInit] }),
     { cancel: !buildOptions.watch },
   );
   if (buildOutput.kind === ResultKind.Failure) {