Angular Google Maps Karma Testing

I updated an Angular project (8 -> 11) and the dependencies. Previously the project used the the @agm/core (https://github.com/SebastianM/angular-google-maps) package, which is not compatible with Angular 11. So I replaced it and followed the suggestions to use the @angular/google-maps directly. Not a big deal, everything working as expected except the tests.

The map is part of an component and the Google API ist loaded there (with prevention of loading it multiple times):

import { Component, OnInit, ViewChild } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { Observable, of } from 'rxjs';
import { catchError, map } from 'rxjs/operators';
import { environment } from 'src/environments/environment';
import { GoogleMap } from '@angular/google-maps';

@Component({
  selector: 'app-map',
  templateUrl: './map.component.html',
  styleUrls: ['./map.component.scss']
})
export class MapComponent implements OnInit {

  @ViewChild(GoogleMap, { static: false }) map: GoogleMap;

  apiLoaded: Observable<boolean>;

  constructor(httpClient: HttpClient) {
    if (window.google === undefined) {
      this.apiLoaded = httpClient.jsonp(`https://maps.googleapis.com/maps/api/js?key=${environment.googleAPIKey}`, 'callback')
          .pipe(
            // Doing preparation stuff
          );
    }
    else {
      this.apiLoaded = of(true);
    }
  }

}

Running ng serve everything is working as expected. But as there are already a lot of tests I ran into problems running ng test:

Unhandled promise rejection: InvalidValueError: ng_jsonp_callback_0 is not a function
error properties: null({ constructor: Function })
Error: 
    at new ge (https://maps.googleapis.com/maps/api/js?key=<api-key>&callback=ng_jsonp_callback_0:70:72)
    at Object._.he (https://maps.googleapis.com/maps/api/js?key=<api-key>&callback=ng_jsonp_callback_0:70:182)
    at Nj (https://maps.googleapis.com/maps/api/js?key=<api-key>&callback=ng_jsonp_callback_0:146:233)
    at https://maps.googleapis.com/maps/api/js?key=<api-key>&callback=ng_jsonp_callback_0:146:118
    at ZoneDelegate.invoke (http://localhost:9876/_karma_webpack_/webpack:/node_modules/zone.js/dist/zone-evergreen.js:364:1)
    at Zone.run (http://localhost:9876/_karma_webpack_/webpack:/node_modules/zone.js/dist/zone-evergreen.js:123:1)
    at http://localhost:9876/_karma_webpack_/webpack:/node_modules/zone.js/dist/zone-evergreen.js:857:1
    at ZoneDelegate.invokeTask (http://localhost:9876/_karma_webpack_/webpack:/node_modules/zone.js/dist/zone-evergreen.js:399:1)
    at Zone.runTask (http://localhost:9876/_karma_webpack_/webpack:/node_modules/zone.js/dist/zone-evergreen.js:167:1)
    at drainMicroTaskQueue (http://localhost:9876/_karma_webpack_/webpack:/node_modules/zone.js/dist/zone-evergreen.js:569:1)

So I guess the Google API is not present during the test. I tried the following things already without any success:

• adding the Google API loading in the index.html:

<script src="https://maps.googleapis.com/maps/api/js?key=YOUR_API_KEY"></script>

• adding the Link to the Karma config file in files section:

    files: [
      'https://maps.googleapis.com/maps/api/js?key=YOUR_API_KEY'
    ],

• downloading the links content, putting it into a file and adding the referenced file in the Karma config in files section. This works for a few times but also throws errors soon ant hus is not a solution for automated testing on Jenkins.
• trying one of the mocks online. The existing tests seem to use a lot of functions there so testing with a mocked API also fails.
• trying to load the API in the test file before running the tests but also not working as expected:

  beforeEach(waitForAsync(() => {
    httpClient.jsonp(`https://maps.googleapis.com/maps/api/js?key=${environment.googleAPIKey}`, 'callback');

I still want to try to move the API loading into a service, but I think this does not change anything. Also downloading the API pre test to load it in the Karma config does not seem to be a good solution either.

How can I ensure to have the current Google Maps API present for testing in an elegant manner?

I fixed it for now with a pretest script:

package.json:

//...
  "scripts": {
    //...
    "pretest": "./pretest.sh",
    "test": "ng test",
//...

The script loads the API code before testing (pretest.sh):

echo "Running 'pretest.sh' script do download Google Maps API for testing..."
rm google-maps-api.js
date +"// Download time: %Y-%m-%d %H:%M" >> google-maps-api.js
curl 'https://maps.googleapis.com/maps/api/js?key=<API_KEY>' >> google-maps-api.js
echo "'pretest.sh' finished"

And Karma loads the file for testing in the karma.config.js files section:

module.exports = function (config) {
  config.set({
    basePath: '',
    plugins: [
      //...
    ],
    files: [
      'google-maps-api.js'
    ],