test(@angular-devkit/build-angular): add test for type checker replacements

Author: filipesilva

packages/angular_devkit/build_angular/test/browser/replacements_spec_large.ts

@@ -6,9 +6,10 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import { runTargetSpec } from '@angular-devkit/architect/testing';
+import { DefaultTimeout, TestLogger, runTargetSpec } from '@angular-devkit/architect/testing';
 import { join, normalize, virtualFs } from '@angular-devkit/core';
-import { takeWhile, tap } from 'rxjs/operators';
+import { of, race } from 'rxjs';
+import { delay, filter, map, take, takeUntil, takeWhile, tap } from 'rxjs/operators';
 import { browserTargetSpec, host } from '../utils';
 
 
@@ -154,4 +155,53 @@ describe('Browser Builder file replacements', () => {
     );
   });
 
+  it('file replacements work with forked type checker on watch mode', async () => {
+    host.writeMultipleFiles({
+      'src/file-replaced.ts': 'export var obj = { one: 1, two: 2 };',
+      'src/file.ts': `export var obj = { one: 1 };`,
+      'src/main.ts': `
+        import { obj } from './file';
+        console.log(obj.two);
+      `,
+    });
+
+    const overrides = {
+      fileReplacements: [{
+        replace: normalize('/src/file.ts'),
+        with: normalize('/src/file-replaced.ts'),
+      }],
+      watch: true,
+    };
+
+    const unexpectedError = `Property 'two' does not exist on type '{ one: number; }'`;
+    const expectedError = `Property 'prop' does not exist on type '{}'`;
+    const logger = new TestLogger('rebuild-type-errors');
+
+    // Race between a timeout and the expected log entry.
+    const stop$ = race<null | string>(
+      of(null).pipe(delay(DefaultTimeout * 2 / 3)),
+      logger.pipe(
+        filter(entry => entry.message.includes(expectedError)),
+        map(entry => entry.message),
+        take(1),
+      ),
+    );
+
+    let errorAdded = false;
+    runTargetSpec(host, browserTargetSpec, overrides, DefaultTimeout, logger).pipe(
+      tap((buildEvent) => expect(buildEvent.success).toBe(true, 'build should succeed')),
+      tap(() => {
+        // Introduce a known type error to detect in the logger filter.
+        if (!errorAdded) {
+          host.appendToFile('src/main.ts', 'console.log({}.prop);');
+          errorAdded = true;
+        }
+      }),
+      takeUntil(stop$),
+    ).subscribe();
+
+    const res = await stop$.toPromise();
+    expect(res).not.toBe(null, 'Test timed out.');
+    expect(res).not.toContain(unexpectedError);
+  });
 });