fix(@angular/build): show unit-test error for missing vitest browser package

When using the experimental `unit-test` builder with the `vitest` runner
and the `browsers` option, an error will now be reported if the `@vitest/browser`
package is not found. Previously, the tests would attempt to execute and
produce a runtime error and stack trace. Now an explicit error with instructions
to install the package will be printed to the console prior to building
and executing the tests.

(cherry picked from commit 9a50040)

Author: clydin

packages/angular/build/src/builders/unit-test/builder.ts

@@ -181,27 +181,17 @@ export async function* execute(
   let instance: import('vitest/node').Vitest | undefined;
 
   // Setup vitest browser options if configured
-  let browser: import('vitest/node').BrowserConfigOptions | undefined;
-  if (normalizedOptions.browsers) {
-    const provider = findBrowserProvider(projectSourceRoot);
-    if (!provider) {
-      context.logger.error(
-        'The "browsers" option requires either "playwright" or "webdriverio" to be installed within the project.' +
-          ' Please install one of these packages and rerun the test command.',
-      );
-
-      return { success: false };
-    }
+  const { browser, errors } = setupBrowserConfiguration(
+    normalizedOptions.browsers,
+    projectSourceRoot,
+  );
+  if (errors?.length) {
+    errors.forEach((error) => context.logger.error(error));
 
-    browser = {
-      enabled: true,
-      provider,
-      instances: normalizedOptions.browsers.map((browserName) => ({
-        browser: browserName,
-      })),
-    };
+    return { success: false };
   }
 
+  // Add setup file entries for TestBed initialization and project polyfills
   const setupFiles = ['init-testbed.js'];
   if (buildTargetOptions?.polyfills?.length) {
     setupFiles.push('polyfills.js');
@@ -252,11 +242,9 @@ export async function* execute(
 }
 
 function findBrowserProvider(
-  projectSourceRoot: string,
+  projectResolver: NodeJS.RequireResolve,
 ): import('vitest/node').BrowserBuiltinProvider | undefined {
-  const projectResolver = createRequire(projectSourceRoot + '/').resolve;
-
-  // These must be installed in the project to be used
+  // One of these must be installed in the project to use browser testing
   const vitestBuiltinProviders = ['playwright', 'webdriverio'] as const;
 
   for (const providerName of vitestBuiltinProviders) {
@@ -267,3 +255,48 @@ function findBrowserProvider(
     } catch {}
   }
 }
+
+function setupBrowserConfiguration(
+  browsers: string[] | undefined,
+  projectSourceRoot: string,
+): { browser?: import('vitest/node').BrowserConfigOptions; errors?: string[] } {
+  if (browsers === undefined) {
+    return {};
+  }
+
+  const projectResolver = createRequire(projectSourceRoot + '/').resolve;
+  let errors: string[] | undefined;
+
+  try {
+    projectResolver('@vitest/browser');
+  } catch {
+    errors ??= [];
+    errors.push(
+      'The "browsers" option requires the "@vitest/browser" package to be installed within the project.' +
+        ' Please install this package and rerun the test command.',
+    );
+  }
+
+  const provider = findBrowserProvider(projectResolver);
+  if (!provider) {
+    errors ??= [];
+    errors.push(
+      'The "browsers" option requires either "playwright" or "webdriverio" to be installed within the project.' +
+        ' Please install one of these packages and rerun the test command.',
+    );
+  }
+
+  if (errors) {
+    return { errors };
+  }
+
+  const browser = {
+    enabled: true,
+    provider,
+    instances: browsers.map((browserName) => ({
+      browser: browserName,
+    })),
+  };
+
+  return { browser };
+}