Выдает ошибку elements.map не является функцией

Question

Когда я пытался запустить приведенный ниже модульный тест, выдает ошибку «elements.map не является функцией» в этой строке const arrayValues = elements.map((val: Element) => this.getAttrval(val));

component.ts, имеющий следующий код:

getAttrval(val: Element): BrowseUri[] {
 console.log(val);
   const href: BrowseUri[] = [];
   let label = val.getAttribute('label');
   let browseUri = val.getAttribute('browseUri');
   let id = val.getAttribute('refId');
   href.push({ label, browseUri, id });
   while (val.hasChildNodes()) {
     val = val.children[0];
     label = val.getAttribute('label');
     browseUri = val.getAttribute('browseUri');
     id = val.getAttribute('refId');
     href.push({ label, browseUri, id });
   }
   console.log(href);
   return href;
 }
 parseWhereusedFilters(data: string): any {
 var data = '<refs id="4005" refCount="3"><node browseUri="/ca:4/" id="4" label="/" refId="" type="ca"><node browseUri="/ca:4/caref:4008/" ext="text/xml" id="4008" label="XXX" refId="4005" type="caref"/><node browseUri="/ca:4/caref:4037/" ext="text/xml" id="4037" label="doczone" refId="4034" type="caref"><node browseUri="/ca:4/caref:4037/caref:4039/" ext="text/xml" id="4039" label="xxx" refId="4016" type="caref"><node browseUri="/ca:4/caref:4037/caref:4039/caref:4021/" ext="text/xml" id="4021" label="xxx" refId="4005" type="caref"/></node></node><node browseUri="/ca:4/caref:4019/" ext="text/xml" id="4019" label="xxx" refId="4016" type="caref"><node browseUri="/ca:4/caref:4019/caref:4021/" ext="text/xml" id="4021" label="xxx" refId="4005" type="caref"/></node></node></refs>';
   const xml = this.xmlParser.parseFromString(data);
   const elements = this.xmlParser['getChildren']('node', xml);
   console.log(elements);
   const arrayValues = elements.map((val: Element) => this.getAttrval(val));
   return arrayValues;
 }

compoenent.spec.ts, имеющий следующий код:

it('should parse the where used data', inject([XmlParser], (xmlParser: XmlParser) => {
   const doc = new Document();
   const refs = doc.createElement('refs');
   for (let i = 0; i < 4; i++) {
     const node = doc.createElement('node');
     refs.appendChild(node);
   }
   doc.appendChild(refs);
let response;
   spyOn(xmlParser, 'parseFromString').and.returnValue(of({response}));
   spyOn(xmlParser, 'getChildren').and.returnValue(of({response}));
   spyOn(component, 'getAttrval').and.returnValue(of({response}));
   const items = component.parseWhereusedFilters('<refs id="4005" refCount="3"><node browseUri="/ca:4/" id="4" label="/" refId="" type="ca"><node browseUri="/ca:4/caref:4008/" ext="text/xml" id="4008" label="xxx" refId="4005" type="caref"/><node browseUri="/ca:4/caref:4037/" ext="text/xml" id="4037" label="doczone" refId="4034" type="caref"><node browseUri="/ca:4/caref:4037/caref:4039/" ext="text/xml" id="4039" label="xxx" refId="4016" type="caref"><node browseUri="/ca:4/caref:4037/caref:4039/caref:4021/" ext="text/xml" id="4021" label="xxx" refId="4005" type="caref"/></node></node><node browseUri="/ca:4/caref:4019/" ext="text/xml" id="4019" label="xxx" refId="4016" type="caref"><node browseUri="/ca:4/caref:4019/caref:4021/" ext="text/xml" id="4021" label="xxx" refId="4005" type="caref"/></node></node></refs>');
   fixture.detectChanges();
   expect(items.length).toEqual(4);
 }));