fix(@angular/build): trigger test re-run on non-spec file changes in watch mode

When non-test files (services, components, etc.) change during watch
mode, use Vitest's module graph to find dependent test specifications
and include them in the re-run set. Previously only direct .spec.ts
file changes triggered test re-runs.

Consolidates the file processing into a single loop for clarity.

Fixes #32159

Author: maruthang

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

@@ -140,8 +140,14 @@ export class VitestExecutor implements TestExecutor {
     let testResults;
     if (buildResult.kind === ResultKind.Incremental) {
       // To rerun tests, Vitest needs the original test file paths, not the output paths.
-      const modifiedSourceFiles = new Set<string>();
+      // Process all modified files in a single loop.
+      const specsToRerun = [];
       for (const modifiedFile of [...buildResult.modified, ...buildResult.added]) {
+        const absoluteOutputFile = this.normalizePath(
+          path.join(this.options.workspaceRoot, modifiedFile),
+        );
+        vitest.invalidateFile(absoluteOutputFile);
+
         // The `modified` files in the build result are the output paths.
         // We need to find the original source file path to pass to Vitest.
         const source = this.entryPointToTestFile.get(modifiedFile);
@@ -150,24 +156,26 @@ export class VitestExecutor implements TestExecutor {
             DebugLogLevel.Verbose,
             `Mapped output file '${modifiedFile}' to source file '${source}' for re-run.`,
           );
-          modifiedSourceFiles.add(source);
+          vitest.invalidateFile(source);
+          const specs = vitest.getModuleSpecifications(source);
+          if (specs) {
+            specsToRerun.push(...specs);
+          }
         } else {
+          // For non-test files (e.g., services, components), find dependent test specs
+          // via Vitest's module graph so that changes to these files trigger test re-runs.
           this.debugLog(
             DebugLogLevel.Verbose,
             `Could not map output file '${modifiedFile}' to a source file. It may not be a test file.`,
           );
-        }
-        vitest.invalidateFile(
-          this.normalizePath(path.join(this.options.workspaceRoot, modifiedFile)),
-        );
-      }
-
-      const specsToRerun = [];
-      for (const file of modifiedSourceFiles) {
-        vitest.invalidateFile(file);
-        const specs = vitest.getModuleSpecifications(file);
-        if (specs) {
-          specsToRerun.push(...specs);
+          const specs = vitest.getModuleSpecifications(absoluteOutputFile);
+          if (specs) {
+            this.debugLog(
+              DebugLogLevel.Verbose,
+              `Found ${specs.length} dependent test specification(s) for non-test file '${absoluteOutputFile}'.`,
+            );
+            specsToRerun.push(...specs);
+          }
         }
       }
 

packages/angular/build/src/builders/unit-test/tests/behavior/watch_rebuild_spec.ts

@@ -20,6 +20,53 @@ describeBuilder(execute, UNIT_TEST_BUILDER_INFO, (harness) => {
       setupApplicationTarget(harness);
     });
 
+    it('should re-run tests when a non-spec file changes', async () => {
+      // Set up a component with a testable value and a spec that checks it
+      harness.writeFiles({
+        'src/app/app.component.ts': `
+          import { Component } from '@angular/core';
+          @Component({ selector: 'app-root', template: '' })
+          export class AppComponent {
+            title = 'hello';
+          }`,
+        'src/app/app.component.spec.ts': `
+          import { describe, expect, test } from 'vitest';
+          import { AppComponent } from './app.component';
+          describe('AppComponent', () => {
+            test('should have correct title', () => {
+              const app = new AppComponent();
+              expect(app.title).toBe('hello');
+            });
+          });`,
+      });
+
+      harness.useTarget('test', {
+        ...BASE_OPTIONS,
+        watch: true,
+      });
+
+      await harness.executeWithCases([
+        // 1. Initial run should succeed
+        ({ result }) => {
+          expect(result?.success).toBeTrue();
+
+          // 2. Modify only the non-spec component file (change the title value)
+          harness.writeFiles({
+            'src/app/app.component.ts': `
+              import { Component } from '@angular/core';
+              @Component({ selector: 'app-root', template: '' })
+              export class AppComponent {
+                title = 'changed';
+              }`,
+          });
+        },
+        // 3. Test should re-run and fail because the title changed
+        ({ result }) => {
+          expect(result?.success).toBeFalse();
+        },
+      ]);
+    });
+
     it('should run tests when a compilation error is fixed and a test failure is introduced simultaneously', async () => {
       harness.useTarget('test', {
         ...BASE_OPTIONS,