test(@angular-devkit/build-angular): add dev-server builder watch option tests

This change adds expanded unit tests for the dev-server builder's `watch` option using the builder test harness.

Author: clydin

packages/angular_devkit/build_angular/src/dev-server/tests/options/watch_spec.ts

@@ -0,0 +1,125 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+import { TimeoutError } from 'rxjs';
+import { concatMap, count, take, timeout } from 'rxjs/operators';
+import { serveWebpackBrowser } from '../../index';
+import {
+  BASE_OPTIONS,
+  BUILD_TIMEOUT,
+  DEV_SERVER_BUILDER_INFO,
+  describeBuilder,
+  setupBrowserTarget,
+} from '../setup';
+
+describeBuilder(serveWebpackBrowser, DEV_SERVER_BUILDER_INFO, (harness) => {
+  describe('Option: "watch"', () => {
+    beforeEach(() => {
+      setupBrowserTarget(harness);
+    });
+
+    it('does not wait for file changes when false', async () => {
+      harness.useTarget('serve', {
+        ...BASE_OPTIONS,
+        watch: false,
+      });
+
+      await harness
+        .execute()
+        .pipe(
+          timeout(BUILD_TIMEOUT * 2),
+          concatMap(async ({ result }, index) => {
+            expect(result?.success).toBe(true);
+
+            switch (index) {
+              case 0:
+                await harness.modifyFile(
+                  'src/main.ts',
+                  (content) => content + 'console.log("abcd1234");',
+                );
+                break;
+              case 1:
+                fail('Expected files to not be watched.');
+                break;
+            }
+          }),
+          take(2),
+        )
+        .toPromise()
+        .catch((error) => {
+          // Timeout is expected if watching is disabled
+          if (error instanceof TimeoutError) {
+            return;
+          }
+          throw error;
+        });
+    });
+
+    it('watches for file changes when not present', async () => {
+      harness.useTarget('serve', {
+        ...BASE_OPTIONS,
+      });
+
+      const buildCount = await harness
+        .execute()
+        .pipe(
+          timeout(BUILD_TIMEOUT * 2),
+          concatMap(async ({ result }, index) => {
+            expect(result?.success).toBe(true);
+
+            switch (index) {
+              case 0:
+                await harness.modifyFile(
+                  'src/main.ts',
+                  (content) => content + 'console.log("abcd1234");',
+                );
+                break;
+              case 1:
+                break;
+            }
+          }),
+          take(2),
+          count(),
+        )
+        .toPromise();
+
+      expect(buildCount).toBe(2);
+    });
+
+    it('watches for file changes when true', async () => {
+      harness.useTarget('serve', {
+        ...BASE_OPTIONS,
+        watch: true,
+      });
+
+      const buildCount = await harness
+        .execute()
+        .pipe(
+          timeout(BUILD_TIMEOUT * 2),
+          concatMap(async ({ result }, index) => {
+            expect(result?.success).toBe(true);
+
+            switch (index) {
+              case 0:
+                await harness.modifyFile(
+                  'src/main.ts',
+                  (content) => content + 'console.log("abcd1234");',
+                );
+                break;
+              case 1:
+                break;
+            }
+          }),
+          take(2),
+          count(),
+        )
+        .toPromise();
+
+      expect(buildCount).toBe(2);
+    });
+  });
+});

packages/angular_devkit/build_angular/src/dev-server/tests/setup.ts

@@ -0,0 +1,40 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+import { buildWebpackBrowser } from '../../browser';
+import { BASE_OPTIONS as BROWSER_BASE_OPTIONS } from '../../browser/tests/setup';
+import { BuilderHarness } from '../../testing/builder-harness';
+import { Schema } from '../schema';
+
+export { describeBuilder } from '../../testing';
+
+export const DEV_SERVER_BUILDER_INFO = Object.freeze({
+  name: '@angular-devkit/build-angular:dev-server',
+  schemaPath: __dirname + '/../schema.json',
+});
+
+/**
+ * Contains all required extract-i18n builder fields.
+ * The port is also set to zero to ensure a free port is used for each test which
+ * supports parallel test execution.
+ */
+export const BASE_OPTIONS = Object.freeze<Schema>({
+  browserTarget: 'test:build',
+  port: 0,
+});
+
+/**
+ * Maximum time for single build/rebuild
+ * This accounts for CI variability.
+ */
+export const BUILD_TIMEOUT = 15000;
+
+export function setupBrowserTarget<T>(harness: BuilderHarness<T>): void {
+  harness.withBuilderTarget('build', buildWebpackBrowser, {
+    ...BROWSER_BASE_OPTIONS,
+  });
+}