Can't resolve all parameters for ApplicationModule: (?)

I just migrated an application module to be an importable library.

I'm trying to make the tests work correctly, just as they worked before, but I get this error:

Error: Can't resolve all parameters for ApplicationModule: (?).
at syntaxError (webpack:///C:/Repositories/MyProject/my-library/node_modules/@angular/compiler/fesm5/compiler.js?:1275:17)
at CompileMetadataResolver._getDependenciesMetadata (webpack:///C:/Repositories/MyProject/my-library/node_modules/@angular/compiler/fesm5/compiler.js?:11176:35)
at CompileMetadataResolver._getTypeMetadata (webpack:///C:/Repositories/MyProject/my-library/node_modules/@angular/compiler/fesm5/compiler.js?:11069:26)
at CompileMetadataResolver.getNgModuleMetadata (webpack:///C:/Repositories/MyProject/my-library/node_modules/@angular/compiler/fesm5/compiler.js?:10937:24)
at CompileMetadataResolver.getNgModuleSummary (webpack:///C:/Repositories/MyProject/my-library/node_modules/@angular/compiler/fesm5/compiler.js?:10747:35)
at eval (webpack:///C:/Repositories/MyProject/my-library/node_modules/@angular/compiler/fesm5/compiler.js?:10861:51)
at Array.forEach (<anonymous>)
at CompileMetadataResolver.getNgModuleMetadata (webpack:///C:/Repositories/MyProject/my-library/node_modules/@angular/compiler/fesm5/compiler.js?:10849:49)
at CompileMetadataResolver.getNgModuleSummary (webpack:///C:/Repositories/MyProject/my-library/node_modules/@angular/compiler/fesm5/compiler.js?:10747:35)
at eval (webpack:///C:/Repositories/MyProject/my-library/node_modules/@angular/compiler/fesm5/compiler.js?:10861:51)

I've seen these possible solutions: Error: Can't resolve all parameters for ApplicationModule: (?) and Cannot resolve parameters for ApplicationModule: (?) but they cannot fix my problem.

projects/my-library/src/test.ts

// This file is required by karma.conf.js and loads recursively all the .spec and framework files

import { getTestBed } from '@angular/core/testing';
import {
  BrowserDynamicTestingModule,
  platformBrowserDynamicTesting
} from '@angular/platform-browser-dynamic/testing';
import 'core-js/es7/reflect';
import 'zone.js/dist/zone';
import 'zone.js/dist/zone-testing';

declare const require: any;

// 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);

Let me know if you need more information to figure out where is the problem.