Revert "update ng 15"

This reverts commit f46c5ce47c.

src/test.ts

@@ -5,6 +5,11 @@ import {getTestBed} from '@angular/core/testing';
 import {BrowserDynamicTestingModule, platformBrowserDynamicTesting} from '@angular/platform-browser-dynamic/testing';
 
 type req = {keys: () => {map: (context: req) => void}};
+declare const require: {context: (a: string, b: boolean, c: RegExp) => req};
 
 // First, initialize the Angular testing environment.
 getTestBed().initTestEnvironment(BrowserDynamicTestingModule, platformBrowserDynamicTesting());
+// Then we find all the tests.
+const context = require.context('./', true, /\.spec\.ts$/);
+// And load the modules.
+context.keys().map(context);