错误：WithCallStack：在打印sinon间谍的第一次调用时

Question

在打印callback.firstCall之后，我在测试中使用sinon。我收到以下errorWithCallStack：错误。我看到其他细节如args，lastargs正确打印了所有这些属性。但是与此同时，还会显示错误消息。我想知道为什么会这样。

spec.js

 .....
const sinon=require('sinon')
const devices ...
describe('servers Route', function() {
    let req;
    let res;
    let mockResponse;
    req = {
         user:{
             id:""
         }
    },

    res = {
    json:sinon.fake()
    }


    it('should mock function',function(){

     var callback=sinon.spy(devices,'getActivatedCustomersResponse');
     devices.getActivatedCustomersResponse(req,res);
     console.log(callback.firstCall);
     //on printing this it shows all the errors
    })

});

错误日志

 errorWithCallStack: Error
    at Function.invoke (C:\cygwin64\home\Portal\node_modules\sinon\lib\sinon\spy.js:312:19)
    at Object.getActivatedCustomersResponse (C:\cygwin64\home\Portal\node_modules\sinon\lib\sinon\spy.js:90:30)
    at Context.<anonymous> (C:\cygwin64\home\Portal\node_modules\server\routes\mock.elastic.spying.spec.js:36:14)
    at callFn (C:\cygwin64\home\Portal\node_modules\node\node-v8.12.0-win-x64\node_modules\mocha\lib\runnable.js:387:21)
    C:\cygwin64\home\Portal\node_modules\mocha\lib\runnable.js:379:7)
    at Runner.runTest (C:\cygwin64\home\Portal\node\node-v8.12.0-win-x64\node_modules\mocha\lib\runner.js:535:10)
    at C:\cygwin64\home\Portal\node\node-v8.12.0-win-x64\node_modules\mocha\lib\runner.js:653:12
    at next (C:\cygwin64\home\Portal\node\node-v8.12.0-win-x64\node_modules\mocha\lib\runner.js:447:14)
    at C:\cygwin64\home\Portal\node\node-v8.12.0-win-x64\node_modules\mocha\lib\runner.js:457:7
    at next (C:\cygwin64\home\Portal\node\node-v8.12.0-win-x64\node_modules\mocha\lib\runner.js:362:14)
    at C:\cygwin64\home\Portal\node\node-v8.12.0-win-x64\node_modules\mocha\lib\runner.js:420:7
    at done (C:\cygwin64\home\Portal\node\node-v8.12.0-win-x64\node_modules\mocha\lib\runnable.js:334:5)
    at callFn (C:\cygwin64\home\Portal\node\node-v8.12.0-win-x64\node_modules\mocha\lib\runnable.js:410:7)
    at Hook.Runnable.run (C:\cygwin64\home\Portal\node\node-v8.12.0-win-x64\node_modules\mocha\lib\runnable.js:379:7)
    at next (C:\cygwin64\home\Portal\node\node-v8.12.0-win-x64\node_modules\mocha\lib\runner.js:384:10)
    at Immediate.<anonymous> (C:\cygwin64\home\Portal\node\node-v8.12.0-win-x64\node_modules\mocha\lib\runner.js:425:5)
    at runCallback (timers.js:810:20)
    at tryOnImmediate (timers.js:768:5)
    at processImmediate [as _immediateCallback] (timers.js:745:5) }