test(@angular-devkit/build-angular): add file replacement watch test

courtesy of @filipesilva

Author: clydin

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

@@ -8,7 +8,7 @@
 
 import { runTargetSpec } from '@angular-devkit/architect/testing';
 import { join, normalize, virtualFs } from '@angular-devkit/core';
-import { tap } from 'rxjs/operators';
+import { debounceTime, take, tap } from 'rxjs/operators';
 import { browserTargetSpec, host } from '../utils';
 
 
@@ -100,4 +100,45 @@ describe('Browser Builder file replacements', () => {
     runTargetSpec(host, browserTargetSpec, overrides)
       .subscribe(undefined, () => done(), done.fail);
   });
+
+  it('file replacements work with watch mode', (done) => {
+    const overrides = {
+      fileReplacements: [
+        {
+          replace: normalize('/src/meaning.ts'),
+          with: normalize('/src/meaning-too.ts'),
+        },
+      ],
+      watch: true,
+    };
+
+    let buildNumber = 0;
+
+    runTargetSpec(host, browserTargetSpec, overrides, 45000).pipe(
+      debounceTime(1000),
+      tap((buildEvent) => expect(buildEvent.success).toBe(true)),
+      tap(() => {
+        const fileName = join(outputPath, 'main.js');
+        const content = virtualFs.fileBufferToString(host.scopedSync().read(fileName));
+        buildNumber += 1;
+
+        switch (buildNumber) {
+          case 1:
+            expect(content).toMatch(/meaning\s*=\s*42/);
+            expect(content).not.toMatch(/meaning\s*=\s*10/);
+            host.writeMultipleFiles({
+              'src/meaning-too.ts': 'export var meaning = 84;',
+            });
+            break;
+
+          case 2:
+            expect(content).toMatch(/meaning\s*=\s*84/);
+            expect(content).not.toMatch(/meaning\s*=\s*42/);
+            break;
+        }
+      }),
+      take(2),
+    ).toPromise().then(() => done(), done.fail);
+  });
+
 });