如何在打字稿中模拟XMLHTTPRequest以进行单元测试

Question

I have this code in my src file and I want to write unit test for this. I am using karma-webpack in angular 4 application. Please suggest

public static load(jsonFile: string): Promise<boolean> {
console.log('calling loadinstance');
return new Promise((resolve: any, reject: any) => {
  const xobj = new XMLHttpRequest();
  xobj.overrideMimeType('application/json');
  xobj.open('GET', jsonFile, true);
  xobj.onreadystatechange = () => {
    const readyOK = 4;
    const responseOK = 200;
    if (xobj.readyState === readyOK) {
      if (xobj.status === responseOK) {
        ConfigLoader.data = JSON.parse(xobj.responseText);
        resolve(true);
      }
      else {
        reject(`Could not load file '${jsonFile}': ${xobj.status}`);
      }
    }
  };
  xobj.send(null);
});

}

Answer 1

Quiet simple use a spyOn.

it('Your Service', inject([YourService], (YourService: yourService) => {
  spyOn(yourService, 'load').and.returnValue(loadedJSON);