How to use the file-saver.default function in file-saver

it('should be using header filename when repseon has [filename]', () => {
      let fn: string;
      const filename = 'newfile.docx';
      spyOn(fs.default, 'saveAs').and.callFake((_body: {}, fileName: string) => (fn = fileName));
      context.fileName = null;
      fixture.detectChanges();
      (dl.query(By.css('#down-docx')).nativeElement as HTMLButtonElement).click();
      const ret = httpBed.expectOne(req => req.url.startsWith('/')) as TestRequest;
      ret.flush(genFile(), {
        headers: new HttpHeaders({ filename }),
      });
      expect(fn!).toBe(filename);
    });

it(`should be down ${ext}`, () => {
        spyOn(fs.default, 'saveAs');
        if (ext === 'docx') context.data = null;
        fixture.detectChanges();
        (dl.query(By.css('#down-' + ext)).nativeElement as HTMLButtonElement).click();
        const ret = httpBed.expectOne(req => req.url.startsWith('/')) as TestRequest;
        ret.flush(genFile());
        expect(fs.default.saveAs).toHaveBeenCalled();
      });
    });

it('should be save zip file', (done: () => void) => {
      spyOn(fs.default, 'saveAs');
      srv.save(zip, { filename: '123.zip' }).then(
        () => {
          expect(fs.default.saveAs).toHaveBeenCalled();
          expect(true).toBe(true);
          done();
        },
        () => {
          expect(false).toBe(true);
          done();
        },
      );
    });
    it('should be call callback', (done: () => void) => {

beforeEach(() => {
      spyOn(fs.default, 'saveAs');
      genModule();
    });
    it('should be export xlsx via array', (done: () => void) => {

.then(() => {
          expect(fs.default.saveAs).toHaveBeenCalled();
          done();
        });
    });

() => {
          expect(fs.default.saveAs).toHaveBeenCalled();
          expect(true).toBe(true);
          done();
        },
        () => {