[DURACOM-240] add and fix tests

src/app/core/shared/math.service.spec.ts

@@ -1,16 +1,54 @@
 import { TestBed } from '@angular/core/testing';
+import {
+  Observable,
+  of,
+} from 'rxjs';
 
-import { MathService } from './math.service';
+import {
+  MathJaxConfig,
+  MathService,
+} from './math.service';
+
+export class MockMathService extends MathService {
+  protected mathJaxOptions: any = {};
+  protected mathJax: MathJaxConfig = { source: '', id: '' };
+  protected mathJaxFallback: MathJaxConfig = { source: '', id: '' };
+
+  protected registerMathJaxAsync(config: MathJaxConfig): Promise<any> {
+    return Promise.resolve();
+  }
+
+  ready(): Observable<boolean> {
+    return of(true);
+  }
+
+  render(element: HTMLElement): void {
+    return;
+  }
+}
 
 describe('MathService', () => {
-  let service: MathService;
+  let service: MockMathService;
 
   beforeEach(() => {
     TestBed.configureTestingModule({});
-    service = TestBed.inject(MathService);
+    service = new MockMathService();
+    spyOn(service, 'render');
   });
 
   it('should be created', () => {
     expect(service).toBeTruthy();
   });
+
+  it('should be ready', (done) => {
+    service.ready().subscribe(isReady => {
+      expect(isReady).toBe(true);
+      done();
+    });
+  });
+
+  it('should render', () => {
+    service.render(document.createElement('div'));
+    expect(service.render).toHaveBeenCalled();
+  });
 });