CODEWITHSUNDEEP
javascriptconsolejasmine
Joe Susnick
Joe Susnick

Reputation: 6772

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.

Upvotes: 13

Views: 32211

Answers (3)

Albert
Albert

Reputation: 39

Please try this,

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

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

describe('test',()=>{
  it("should test for the function_to_test's console output", ()=>{
    const logSpy = spyOn(console, 'log')
    function_to_test ()
    expect(logSpy.calls.count()).toBe(2) // "console.log" called twice
    expect(logSpy.calls.all()[0].args[0]).toBe("Nicholas") 
    expect(logSpy.calls.all()[1].args[0]).toBe(29)
  })
})

Hope it helps,

thanks

Upvotes: 0

Esaith
Esaith

Reputation: 808

I know this is an old question (7+ years old) but I just came upon this answer today through Google search. From this answer, I changed it to the following and has worked for me.

spyOn(console, 'error');
const dto = new DTO();  // add to console.error if no parameter is given
expect(console.error).toHaveBeenCalled();

Upvotes: 6

Jason
Jason

Reputation: 1969

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 });
});

Upvotes: 27

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