refactor(@angular-devkit/build-angular): clean up SingleTestTransformLoader

Minor cleanup of SingleTestTransformLoader and fix interface issue which causes  #17823 to be red.

Author: alan-agius4

packages/angular_devkit/build_angular/src/angular-cli-files/plugins/single-test-transform.ts

@@ -5,14 +5,15 @@
  * 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 { logging } from '@angular-devkit/core';
+import { logging, tags } from '@angular-devkit/core';
 import { getOptions } from 'loader-utils';
 import { extname, join } from 'path';
 import { loader } from 'webpack';
 
 export interface SingleTestTransformLoaderOptions {
-  files: string[]; // list of paths relative to main
-  logger: logging.Logger;
+  /* list of paths relative to the entry-point */
+  files?: string[];
+  logger?: logging.Logger;
 }
 
 export const SingleTestTransformLoader = require.resolve(join(__dirname, 'single-test-transform'));
@@ -30,29 +31,24 @@ export const SingleTestTransformLoader = require.resolve(join(__dirname, 'single
  * Then it adds import statements for each file in the files options
  * array to import them directly, and thus run the tests there.
  */
-export default function loader(this: loader.LoaderContext, source: string) {
-  const options = getOptions(this) as SingleTestTransformLoaderOptions;
-  const lineSeparator = process.platform === 'win32' ? '\r\n' : '\n';
+export default function loader(this: loader.LoaderContext, source: string): string {
+  const { files = [], logger = console } = getOptions(this) as SingleTestTransformLoaderOptions;
+  // signal the user that expected content is not present.
+  if (!source.includes('require.context(')) {
+    logger.error(tags.stripIndent
+      `The 'include' option requires that the 'main' file for tests includes the below line:
+      const context = require.context('./', true, /\.spec\.ts$/);
+      Arguments passed to require.context are not strict and can be changed.`);
+
+    return source;
+  }
 
-  const targettedImports = options.files
+  const targettedImports = files
     .map(path => `require('./${path.replace('.' + extname(path), '')}');`)
-    .join(lineSeparator);
-
-  // TODO: maybe a documented 'marker/comment' inside test.ts would be nicer?
-  const regex = /require\.context\(.*/;
-
-  // signal the user that expected content is not present
-  if (!regex.test(source)) {
-    const message = [
-      `The 'include' option requires that the 'main' file for tests include the line below:`,
-      `const context = require.context('./', true, /\.spec\.ts$/);`,
-      `Arguments passed to require.context are not strict and can be changed`,
-    ];
-    options.logger.error(message.join(lineSeparator));
-  }
+    .join('\n');
 
-  const mockedRequireContext = 'Object.assign(() => { }, { keys: () => [], resolve: () => undefined });' + lineSeparator;
-  source = source.replace(regex, mockedRequireContext + targettedImports);
+  const mockedRequireContext = 'Object.assign(() => { }, { keys: () => [], resolve: () => undefined });\n';
+  source = source.replace(/require\.context\(.*/, mockedRequireContext + targettedImports);
 
   return source;
 }

packages/angular_devkit/build_angular/src/karma/selected_spec.ts

@@ -62,7 +62,7 @@ describe('Karma Builder', () => {
       expect(lastErrorLogEntry && lastErrorLogEntry.message)
         // tslint:disable-next-line:max-line-length
         .toContain(
-          "The 'include' option requires that the 'main' file for tests include the line below:",
+          "The 'include' option requires that the 'main' file for tests includes the below line:",
         );
 
       await run.stop();