test(@angular-devkit/build-ng-packagr): add tests for watch mode

Author: alan-agius4

packages/angular_devkit/build_ng_packagr/src/build/index_spec_large.ts

@@ -8,9 +8,8 @@
 
 import { TargetSpecifier } from '@angular-devkit/architect';
 import { TestProjectHost, runTargetSpec } from '@angular-devkit/architect/testing';
-import { join, normalize } from '@angular-devkit/core';
-import { tap } from 'rxjs/operators';
-
+import { join, normalize, virtualFs } from '@angular-devkit/core';
+import { debounceTime, map, take, tap } from 'rxjs/operators';
 
 const devkitRoot = normalize((global as any)._DevKitRoot); // tslint:disable-line:no-any
 const workspaceRoot = join(devkitRoot, 'tests/angular_devkit/build_ng_packagr/ng-packaged/');
@@ -43,4 +42,59 @@ describe('NgPackagr Builder', () => {
       tap((buildEvent) => expect(buildEvent.success).toBe(true)),
     ).toPromise().then(done, done.fail);
   });
+
+  it('rebuilds on TS file changes', (done) => {
+    const targetSpec: TargetSpecifier = { project: 'lib', target: 'build' };
+
+    const goldenValueFiles: { [path: string]: string } = {
+      'projects/lib/src/lib/lib.component.ts': `
+      import { Component } from '@angular/core';
+
+      @Component({
+        selector: 'lib',
+        template: 'lib update works!'
+      })
+      export class LibComponent { }
+      `,
+    };
+
+    const overrides = { watch: true };
+
+    let buildNumber = 0;
+
+    runTargetSpec(host, targetSpec, overrides)
+    .pipe(
+      // We must debounce on watch mode because file watchers are not very accurate.
+      // Changes from just before a process runs can be picked up and cause rebuilds.
+      // In this case, cleanup from the test right before this one causes a few rebuilds.
+      debounceTime(1000),
+      tap((buildEvent) => expect(buildEvent.success).toBe(true)),
+      map(() => {
+        const fileName = './dist/lib/fesm5/lib.js';
+        const content = virtualFs.fileBufferToString(
+          host.scopedSync().read(normalize(fileName)),
+        );
+
+        return content;
+      }),
+      tap(content => {
+        buildNumber += 1;
+        switch (buildNumber) {
+          case 1:
+            expect(content).toMatch(/lib works/);
+            host.writeMultipleFiles(goldenValueFiles);
+            break;
+
+          case 2:
+            expect(content).toMatch(/lib update works/);
+            break;
+          default:
+            break;
+        }
+      }),
+      take(2),
+    )
+    .toPromise()
+    .then(done, done.fail);
+  });
 });