Take screenshot from Karma while running tests in PhantomJS 2?

Question

I need a way to take a screenshot during a test which uses QUnit and Karma to run inside PhantomJS 2.0.1

I've found this command:

window.top.callPhantom('render');

That doesn't throw any error but doesn't seem to work, or at least, I don't know where to look for the taken screenshot.

Any clue?

Tubb

Answer 1

Found a way!

Solution

I had to edit my custom PhantomJS custom launcher adding an option:

PhantomJSCustom: {
    base: 'PhantomJS',
    options: {
        onCallback: function(data){
            if (data.type === "render") {
                // this function will not have the scope of karma.conf.js so we must define any global variable inside it
                if (window.renderId === undefined) { window.renderId = 0; }
                page.render(data.fname || ("screenshot_" + (window.renderId++) + ".png"));
            }
        }
    }
}

As you can see, we are defining the onCallback option, it will be injected inside the script launched by phantomjs. The script, then, will contain:

page.onCallback = <our function>

Now, we are able to use callPhantom to ask PhantomJS to run the content of our onCallback function and use all the native PhantomJS methods.

Usage

Now, you can use in your tests the function:

window.top.callPhantom({type: 'render'});

To take a screenshot that will be saved in the root directory of your application.

Additionally, if you define the fname you'll be able to define a custom path and file name to your screenshot.

window.top.callPhantom({type: 'render', fname: '/tmp/myscreen.png'});

---

Pack all together for ease of use

I've created an handy function to use inside my tests. The onCallback function is reduced to the minimum necessary, in this way all the logic is managed inside my test environment:

karma.conf.js

PhantomJSCustom: {
    base: 'PhantomJS',
    options: {
        onCallback: function(data){
            if (data.type === 'render' && data.fname !== undefined) {
                page.render(data.fname);
            }
        }
    }
}

helper

// With this function you can take screenshots in PhantomJS!
// by default, screenshots will be saved in .tmp/screenshots/ folder with a progressive name (n.png)
var renderId = 0;
function takeScreenshot(file) {
    // check if we are in PhantomJS
    if (window.top.callPhantom === undefined) return;

    var options = {type: 'render'};
    // if the file argument is defined, we'll save the file in the path defined eg: `fname: '/tmp/myscreen.png'
    // otherwise we'll save it in the default directory with a progressive name
    options.fname = file || '.tmp/screenshots/' + (renderId++) + '.png';

    // this calls the onCallback function of PhantomJS, the type: 'render' will trigger the screenshot script
    window.top.callPhantom(options);
}

---

Credits

I got this script from this answer, adapted it and found by myself where to put it to make it work with karma.

Tubb

Great stuff! I am curious, where did you find a good place to add the helper function that is common? – Overwhelm

Using karma and qunit, we have some files that are loaded before the tests we use to load all this kind of helpers. – Tubb

Answer 2

My Karma entry for a customized phantomjs that takes snapshots looked like this:

module.exports = function (config) {
  config.set({
    ..
    browsers: [ 'PhantomJSCustom'],
    customLaunchers: {
      'PhantomJSCustom': {
        base: 'PhantomJS',
        options: {
          onCallback: function(data){
            if (data.type === "render") {
              // this function will not have the scope of karma.conf.js so we must define any global variable inside it
              if (window.renderId === undefined) { window.renderId = 0; }
              page.render(data.fname || ("screenshot_" + (window.renderId++) + ".png"));
            }
          }
        }
      }
    },
    phantomjsLauncher: {
      // Have phantomjs exit if a ResourceError is encountered (useful if karma exits without killing         // phantom)
      exitOnResourceError: true
    },
    ..
  })

Cl