Joe Susnick Joe Susnick - 2 months ago 10
Javascript Question

How can I use jasmine.js to test for console output?

I'm working through the text: Professional JavaScript for Web Developers by Nicholas Zakas
and I'm testing the examples with Jasmine.js.

I can currently test the output of a function by specifying a return a value, but I'm running into trouble when there are multiple pieces of data that I want to return.

The textbook uses the alert() method, but this is cumbersome and I don't know how to test for alerts. I was wondering if there was a way to test for console.log() output. For instance:

function_to_test = function(){
var person = new Object();
person.name = "Nicholas";
person.age = 29;

return(person.name); //Nicholas
return(person.age); //29
});


I know I can have them return as one string, but for more complicated examples I'd like to be able to test the following:

function_to_test = function(){
var person = new Object();
person.name = "Nicholas";
person.age = 29;

console.log(person.name); //Nicholas
console.log(person.age); //29
});


The Jasmine test looks something like:

it("should test for the function_to_test's console output", function(){
expect(function_to_test()).toEqual("console_output_Im_testing_for");
});


Is there a simple way to do this that I'm just missing? I'm pretty new to coding so any guidance would be appreciated.

Answer

There are a couple of things that are wrong with your code above. As pointed out, having multiple return statement will not work. Also, when defining a new object, it is preferable to use the object literal syntax over using new Object.

What you would normally do is something more like this:

var function_to_test = function () {
  var person = {
    name : "Nicholas",
    age : 29
  };

  return person;
};

Using the function above, there are a couple of ways you could test this. One it to mock out the console.log object using Jasmine Spies.

it("should test for the function_to_test's console output", function () {
    console.log = jasmine.createSpy("log");
    var person = function_to_test();
    expect(console.log).toHaveBeenCalledWith(person);
});

The other is to test the actual output of the function.

it("should return a person", function () {
    var person = function_to_test();
    expect(person).toEqual({ name : "Nicholas", age : 29 });
});
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