fix(@angular/build): enable code splitting for vitest browser tests

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

@@ -256,13 +256,13 @@ export async function getVitestBuildOptions(
     sourceMap: { scripts: true, vendor: false, styles: false },
     outputHashing: adjustOutputHashing(baseBuildOptions.outputHashing),
     optimization: false,
+    namedChunks: false,
     entryPoints,
-    // Every spec file is its own entry point, so splitting hoists any module shared between two
-    // specs into a chunk whose exports are then read across a chunk boundary. Those reads rely on
-    // live ESM bindings, and a module placed in a shared chunk is only assigned its exported value
-    // when that chunk's lazy initializer runs, so an importing chunk can read `undefined`. Nothing
-    // downloads these bundles, so there is no benefit to weigh against that.
-    disableCodeSplitting: true,
+    // Vitest's Node-based module loading emulation (vite-node) is not fully spec compliant and lacks
+    // live ESM bindings across chunk boundaries. This can cause uninitialized exports or break mocking.
+    // In browser tests, however, the real browser adheres to the ECMAScript spec, so code splitting can
+    // be safely enabled.
+    disableCodeSplitting: options.browsers?.length ? false : true,
     // Enable support for vitest browser prebundling. Excludes can be controlled with a runnerConfig
     // and the `optimizeDeps.exclude` option.
     externalPackages: true,

packages/angular/build/src/tools/esbuild/angular/compiler-plugin.ts

@@ -576,9 +576,7 @@ export function createCompilerPlugin(
             const replacement = pluginOptions.fileReplacements?.[path.normalize(args.path)];
             if (replacement) {
               return {
-                contents: await import('node:fs/promises').then(({ readFile }) =>
-                  readFile(path.normalize(replacement)),
-                ),
+                contents: await readFile(path.normalize(replacement)),
                 loader: 'json' as const,
                 watchFiles: [replacement],
               };