how to handle sinon.stub().throws() in unit test by Sinon JS - angularjs

Question

Am trying to invoke fail condition in my snippet.
But when I use sinon.stub().throws() method It shows me error.
Am unable to handle it in code.
Here is my snippet:
login() {
let loginData = this.loginData;
return this.authService.login(loginData).then(userData => {
let msg = `${this.niceToSeeYouAgain} ${userData.email}!`;
this.userAlertsService.showSuccessToast(msg);
this.navigationService.afterLoggedIn();
//above lines are covered in test cases
}, errorInfo => {
// below line are needed to test
this.userAlertsService.showAlertToast(errorInfo);
});
}
**And here is my unit-test snippet: **
it('.login() - should throw exception - in failure case', sinon.test(() => {
let errorInfo = "some error";
let stub = sinon.stub(authService, 'login').throws();
let spy1 = sinon.spy(controller.userAlertsService, 'showAlertToast');
//call function
controller.login();
// $timeout.flush();
// expect things
console.log(stub.callCount, stub.args[0]);
}));
Please let me know what am doing wrong

Answer 1

You need to wrap the function that you know is going to fail, and then call it. e.g.
it('handles errors in methodThatCallsAnotherFailingMethod', function() {
error = new Error("some fake error");
sandbox.stub(SomeObject, "doSomething").throws(error);
call = function() {
// methodThatCallsAnotherFailingMethod calls SomeObject.doSomething()
methodThatCallsAnotherFailingMethod();
};
expect(call).to.throw(Error);
});
When testing (or spying on) other stuff in methodThatCallsAnotherFailingMethod you can do this in your test:
try {
call();
} catch (error) {
expect(MySpy).to.have.been.calledWith(error);
}

Answer 2

This question is a month old as of this answer, but I encountered a similar error, and Google hasn't yielded any explanation for this behavior. I wanted to test the failure branch of my login as well, and stub.throws() actually threw the error (causing the test to fail) instead of rejecting the login promise. If anyone knows why this happens, I'd appreciate it.
In any case, this is what worked for me:
let d = Q.defer(); // Or whichever promise library you use
d.reject(); // Force the promise to fail
let stub = sinon.stub(authService, 'login').returns(d.promise); // Should do what you want
// The rest of the test