During my test with mocha and sinon, I encountered an issue where I couldn't retrieve a callback value from inside a promise scope of an HTTP-request due to the asynchronous nature of promises. It seems that by the time sinon.spy checks on the callback, it has already vanished or become empty/undefined. Below is the testing code snippet:
it('should issue GET /messages ', function() {
server.respondWith('GET', `${apiUrl}/messages?counter=0`, JSON.stringify([]));
let callback = sinon.spy();
Babble.getMessages(0, callback);
server.respond();
sinon.assert.calledWith(callback, []);
});
Here's the promise in question:
function requestPoll(props) {
return new Promise(function(resolve, reject) {
var xhr = new XMLHttpRequest();
xhr.open(props.method, props.action);
xhr.timeout = 500; // time in milliseconds
if (props.method === 'post' ) {
xhr.setRequestHeader('Content-Type', 'application/json');
}
xhr.addEventListener('load', function(e) {
resolve(e.target.responseText);
});
xhr.send(JSON.stringify(props.data));
});
}
and the call which I'm trying to get a callback from using sinon.spy
getMessages: function(counter, callback){
requestPoll({
method: "GET",
action: "http://localhost:9090/messages?counter="+counter
}).then(function(result){
callback(result);
});
}
The issue lies in sinon.spy not receiving any arguments (due to the async functionality). I attempted to find a way to extract the result outside the scope and assign it to the callback, but it proved impossible. I also tried using resolve and promise return methods but found no success.
How can I ensure this unit test passes?
Edit:
this is my attempt:
getMessages: function(counter, callback){
var res;
res = httpRequestAsync("GET",'',"http://localhost:9097/messages?counter=",counter);
console.log(res);
if(res!="")
callback( JSON.parse(res) );
}
I moved the request to a separate function:
function httpRequestAsync(method,data,theUrl,counter)
{
return requestPoll({
method: method,
action: theUrl+counter,
data: data
}).then(JSON.parse);
}
It returned res as the promise and within its prototype contains the promised value required.
https://i.sstatic.net/ZKc36.png
Is there a way to access that promised value successfully?