fix(@angular/build): resolve test files correctly on Windows when using non-C drives

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

@@ -229,6 +229,10 @@ export function createVitestPlugins(pluginOptions: PluginOptions): VitestPlugins
         // Construct the full, absolute path and normalize it to POSIX format.
         const fullPath = toPosixPath(path.join(baseDir, id));
 
+        if (testFileToEntryPoint.has(fullPath)) {
+          return fullPath;
+        }
+
         // Check if the resolved path corresponds to a known build artifact.
         const relativePath = path.relative(workspaceRoot, fullPath);
         if (buildResultFiles.has(toPosixPath(relativePath))) {

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

@@ -129,7 +129,7 @@ export function generateNameFromPath(
   roots: string[],
   removeTestExtension: boolean,
 ): string {
-  const relativePath = removeRoots(testFile, roots);
+  const relativePath = removeRoots(testFile, roots.map(toPosixPath));
 
   let startIndex = 0;
   // Skip leading dots and slashes

tests/e2e/tests/vitest/windows-subst-drive.ts

@@ -0,0 +1,66 @@
+import assert from 'node:assert/strict';
+import * as fs from 'node:fs';
+import * as path from 'node:path';
+import { execAndCaptureError, silentExec } from '../../utils/process';
+import { applyVitestBuilder } from '../../utils/vitest';
+import { stripVTControlCharacters } from 'node:util';
+
+export default async function (): Promise<void> {
+  // This test uses `subst` to map the project directory to a virtual drive letter
+  // to simulate running tests from a non-C drive on Windows.
+  if (process.platform !== 'win32') {
+    return;
+  }
+
+  await applyVitestBuilder();
+
+  const originalCwd = process.cwd();
+  const driveLetter = 'X:'; // Pick a drive letter that is unlikely to be in use.
+
+  try {
+    // 1. Map the parent directory of the project to the virtual drive.
+    // This avoids running the project from the root of the drive (X:\), which can cause
+    // issues with workspace detection.
+    const projectParentDir = path.dirname(originalCwd);
+    const projectName = path.basename(originalCwd);
+
+    await silentExec('subst', driveLetter, projectParentDir);
+
+    // 2. Change the current process's working directory to the project folder on the virtual drive.
+    const newCwd = path.join(driveLetter + '\\', projectName);
+    process.chdir(newCwd);
+
+    // Verify that the file system mapping is working as expected.
+    assert(fs.existsSync('angular.json'), 'angular.json should exist on the subst drive');
+
+    // 3. Run `ng test`.
+    // We expect this to fail with NG0203 in the subst environment due to dual-package hazards
+    // (Angular loading from both X: and D:) within bazel. However, the failure proves that the
+    // test file was discovered and loaded.
+    const error = await execAndCaptureError('ng', ['test', '--watch=false']);
+    const output = stripVTControlCharacters(error.message);
+
+    console.log('OUTPUT:', output);
+
+    // 4. Verify that Vitest found the test file and identified the tests within it.
+    assert.match(
+      output,
+      /src\/app\/app\.spec\.ts \(2 tests/,
+      'Expected tests to be discovered and loaded, even if execution fails due to subst aliasing.',
+    );
+  } finally {
+    // 5. Teardown: Restore CWD and remove the virtual drive mapping.
+    try {
+      process.chdir(originalCwd);
+    } catch (e) {
+      console.error('Failed to restore CWD:', e);
+    }
+
+    try {
+      await silentExec('subst', driveLetter, '/d');
+    } catch (e) {
+      // Ignore errors if the drive wasn't mounted or if unmount fails (best effort)
+      console.error(`Failed to unmount ${driveLetter}:`, e);
+    }
+  }
+}