Visual Regression with Galen

By soumyajit.basu Jan 15, 2017

Galen is an open source layout testing tool for software applications, which helps us test the look and feel of the application. The idea behind using Galen is to simplify layout testing where we won’t need to manually test an application for UI based issues. Galen can also be used to automate UI regression.


Currently Galen is a fully functional testing framework with rich reporting and test management system. It supports both Javascript and Java. It has its own syntax called Galen specs for describing the positioning and alignment of elements on a web page. It uses Selenium to interact with the page objects.

Here's a Galen framework tutorial that'll help make sense of the tool, and all the concepts involved.

We also have a quick video which will take you through all the steps and concepts explained in this blog.


Responsiveness of a Browser

The framework is designed to test the responsiveness of an application. It is easy to set up Galen to test the responsiveness of an application for different browsers and for multiple devices. Galen initiates a browser, and resizes it to a defined resolution which can be passed as a parameter when writing the tests. It can then test the responsiveness according to the specifications defined.

Runs on Cloud and Selenium

Galen has been made flexible enough to run on third-party cloud services such as BrowserStack and Sauce Labs. The tests can also be run using Selenium Grid. This would help save time when running tests on multiple devices.



For executing Galen the Java version should be 1.8.

NPM based installation

For npm based installation, just type in the command sudo npm install -g galenframework-cli

Manual Installation

Install on OS X and Linux

  • Download the archive from Download Page and extract it in any directory. Go to the extracted directory of the galen and execute the following command: sudo ./
  • To check whether Galen is successfully installed execute the following command: galen -v.

The above command should print the installed version of Galen within your system.

Configuring Galen

To configure Galen, create a project directory and inside that, execute the following command: galen config

This would basically create a galen.config file in your project directory which would contain the configurational parameters for Galen. You need to configure the ChromeDriver for Chrome and the GeckoDriver for Firefox. To execute your tests in headless mode you can also execute it using PhantomJs.

To configure the drivers use the following syntax:


Nota Bene

In case of drivers, instead of using the driver executables for chrome, phantomjs, and firefox, you can also install them in your local machine.
Since I am using a Mac I will be using Homebrew to install the drivers.
1. To execute your tests on firefox you will need the geckodriver. Gecko driver can be installed by using brew install geckdriver. This will install the latest stable version of gecko driver in your system.
2. To execute your tests on chrome you will need the chromedriver. Chrome driver can be installed by using brew install chromedriver. This will install the latest stable version of chrome driver in your system.
3. To execute your tests headlessly you will need the phantomjs driver which can be installed in your system using brew install phantomjs.

Once this is done you just need to give the path of the driver in your galen.config file. This will look something like this:


Modus Operandi3-706014603879248525

Galen operates in the following manner.

  • Galen opens a page in a browser
  • Resizes the browser to a specific size
  • Tests the layout with Galen specs

In case the page is not directly accessible, Galen allows you to perform some operations on the website first. As it is based on Selenium, all operations related to clicking, typing, injecting client-side JavaScript can be done very easily.

Galen specs is the language with which the specifications of responsiveness can be defined as per different devices. The following code snippet will give an idea of how easy it is to implement the page specifications using Galen.

= Main section =
     height 100px
     inside screen 0px top
     width 100% of screen/width

     height 50 to 60px
     width 100% of screen/width
     below header ~ 0px

     inside menu 20 to 50px left, 0 to 10px top

    @on mobile
        width 100px

    @on desktop
        width 150px

Project Structure

This would be the possible project directory structure.

1. Drivers directory consists of the browser kits required to execute a browser. This directory includes GeckoDriver, ChromeDriver and PhantomjsDriver.

2. PageInteractions directory contains all the JavaScript related logic related to page interactions.

3. Reports directory consists of all the reports executed on Cross Devices, Cross Browsers and specific to only a single device.

  • Cross_Browser_Specs_reports which has the reports for Cross Browsing based test executions
  • Cross_Device_Specs_Reports which has the reports for Cross Browsing and Cross Device based test execution
  • Uni_Specs_Reports which has the reports for tests executed specific to a single device

4. Specs directory consists of the Galen specifications and has two classifications:

  • Cross_Specs which essentially focuses on the characteristics on multiple devices
  • Uni_Specs focuses on the characteristics of a single device

5. Test_Suites directory consists of the test suites required to execute all the tests and has two classifications.

  • Cross_Browser which focuses on tests written for multiple browser and multiple devices
  • Cross_Devices which focuses on tests written for multiple devices only specific to the default browser mentioned in the galen configuration
  • Uni_Devices which focuses on tests written specific to the device that's specific to the default browser mentioned in the galen configuration only

6. galen.config consists of all the configuration related parameters required to execute Galen.

Galen Specs2-9

Galen specs language is quite flexible and gives the opportunity to express exactly how you want your website to behave on different devices and on different browsers. There are two main parts in page specs file:

Object definition

Each Galen spec file normally starts with object definition. It is the place where you give names to page objects and also define the so called locators – the way for Galen to find element on test page. The available locators are:

  • id – searches for object by id in DOM
  • css – uses CSS selectors to find objects
  • xpath – uses XPathexpressions

The object definition is defined with @objects keyword and all objects are declared below it. The object definition can be defined as follows:

 header      css
 header-logo css div:nth-child(2) a img.cgu-logo
 carousel    id  hero-carousel-mob

Object Specs

The object specs consists of the specifications of the page object. You can consider your object specs to be an assertion. Object specs are the validation metrics for the page objects. Based on the object specs the validation for the visual regression is carried out.

   height 50px
   width 375px
   height 33px
   width 41px

Sections and Tagging

Sections are declared with = symbol in the beginning and end of the line. Also in Galen you can have multiple sections within each other. This allows you to structure your test code so that it is easier to read the specs.

= Header section =
     height 50px
     width 375px
     height 33px
     width 41px

Quite often you need to declare different specs for different conditions (e.g. various devices like mobile, tablet, desktop etc.). You can specify tags in your spec file so that it is easier to manage your layout testing. You can wrap all your checks inside @on statement like this:

@on mobile
   height 50px
   width 375 to 410px

@on desktop
   height 40px
   width 1024px


One of the simplest specs in Galen. It doesn’t take any parameters. It is used to check that the element is either missing on page (in HTML code) or it is present but not visible (e.g. style display:none)



Spec inside verifies that an element is visually inside another element.

 inside site-nav 10px top


The basis for all specs is a so called “range”. Range is a format of defining boundaries for any value. With the range you may express that the expected value should be exactly ‘0’, or greater than ‘0’, less then ‘0’ etc. For example

# The value between range
width 375 to 400px
# Greater than
width > 40 px
# Less than
width < 40 px
# Greater than or equals
width >= 40 px
# Less than or equals
width <= 40 px
# Approximate
width ~ 100 px

Galen Test Suite3-3

To give more flexibility and maintainability to the user, Galen came up with another simple format for defining test suites. Test suites are just a set of pages that need to be checked with the appropriate test specs. But there is something more in there which gives a lot of power in testing. Apart from this it also makes the test execution much smoother.

The aim of deploying a test suite is mainly to carry out continuous executions of all the test specification without human intervention and Galen  provides such ease through its deployment of the test suite. The entire specification of the application can be executed at one go.

Basic Format

The basic format of the test suite looks something like this.

Checking the responsiveness for business section on ${device}
    Business section | http://${domain}/business ${resolution}
       wait 10s until exist "css: div#nebula_div_btn"
       check ././Specs/Uni_Specs/CGU_Business.gspec

Defining the basic format of a test suite in Galen takes place in three simple steps:

  • Defining the name of the test. For this test we have also specified to run these against a specific domain and platform with the browser resize resolution.
  • If there are any conditions that needs to be provided or if you need to call an external JavaScript file to define the Page Interactions that can be written onto the second step.
  • In the third step you define the Page Action which basically tells to check the page specification for the particular url defined.

Passing JavaScript variable to a spec file

You can pass some data from your tests into your spec file so that they are accessible from JavaScript statements. To do this you need to pass it via --VvariableName variableValue argument. For example:

Home page test 1024x768
        check homepage.gspec --include desktop --Vusername John


It is always nice to put commonly used data in variables. e.g. we can put domain name in the variable. This can be done with special instruction: set

@@ set
  resolution 375x667
  set device Iphone6

@@ groups Business_Section
Checking the responsiveness for business section on ${device}
  Business section | HTTP://${domain}/business $ {resolution}
    wait 10s until exist "css: div#nebula_div_btn"
    check ././Specs/Uni_Specs/CGU_Business.gspec
Or you can also use variable reference when defining another variable.

@@ set
    base_url       HTTP://${domain}/ 

Home page on a small mobile device
    ${base_url} 320x600
        check   homepage.gspec --include "mobile,all" --exclude "nomobile"

Replacing Page URL in reports

Once the test is done Galen will generate a HTML report and use the browser factory that you defined in your spec. If you would like to change the way it appears there you can use ‘|’ symbol like in the following example:

Checking the responsiveness for menu in the business section on ${device}
  Breadcrumb in Business section | HTTP://${domain}/business ${resolution}

In the end galen will use everything before ‘|’ in HTML report. So only the Breadcrumb in Business section part will be shown.


If you want to run tests against different devices or different browsers, you can write a data table and mark the test with “parameterized” special instruction. This can be done using the @@ parameterized annotation.

@@ parameterized
    | deviceName | tags      | size     |
    | Mobile     | mobile    | 320x600  |
    | Tablet     | tablet    | 640x480  |
    | Desktop    | desktop   | 1024x800 |
Home page on ${deviceName} device ${size}
        check homepage.gspec --include "${tags}"

As you can see, we defined a data table where the first row is used as a header with names of parameters. Using the example above Galen will run test 3 times with all listed parameters. In the report you will see the tests runs like this:

Home page on Mobile device
Home page on Tablet device
Home page on Desktop device

We can also parameterize the already existing parameterized tests in the suite. This can be done in the following way:

@@ parameterized
    | browser  |
    | firefox  |
    | chrome   |
    | ie       |
@@ parameterized
    | deviceName | tags      | size     |
    | Mobile     | mobile    | 320x600  |
    | Tablet     | tablet    | 640x480  |
    | Desktop    | desktop   | 1024x800 |
Home page on ${deviceName} device in ${browser} browser
    ${browser} ${size}
        check homepage.gspec --include "${tags}"


Tables comes in handy when we want to parameterize all the tests running within the test suite. It would look something like this:

@@ table devices
    | deviceName | tags      | size     |
    | Mobile     | mobile    | 320x600  |
    | Tablet     | tablet    | 640x480  |
    | Desktop    | desktop   | 1024x800 |

@@ parameterized using devices
Home page on ${deviceName} device
        check homepage.gspec --include "${tags}"

@@ parameterized using devices
Login page on ${deviceName} device
  HTTP:// ${size}
        check login.gspec --include "${tags}"

You can also merge tables inside your parameterization code block:

@@ table deviceList_A
    | deviceName | tags      | size     |
    | Mobile     | mobile    | 320x600  |
    | Tablet     | tablet    | 640x480  |
    | Desktop    | desktop   | 1024x800 |

@@ table deviceList_B
    | deviceName | tags      | size     |
    | Mobile 2   | mobile    | 360x600  |
    | Mobile 3   | mobile    | 400x600  |
    | Mobile 4   | mobile    | 500x600  |

@@ parameterized using deviceList_A, deviceList_B
Login page on ${deviceName} device
   HTTP:// ${size}
        check login.gspec --include "${tags}"

Disabling a test

A test can be disabled in Galen using the @@ disable annotation.

@@ disabled
Home page
     HTTP://    640x480
        check homepage.gspec

Login page
        check homepage.gspec

Test Groups

Since version 1.6 you can tag your tests with groups. That will allow you to group your tests in HTML report and choose which group to run in command line. To mark a specific test as a group just use groups keyword:

@@ groups Business_Section
Checking the responsiveness for business section in ${browser} browser on ${deviceName}
  selenium ${browser}http://${domain}/business ${size}
  wait 10s until exist "css: div#nebula_div_btn"
  check ././Specs/Cross_Specs/CGU_Business.gspec --include "${tags}"

Waiting for Dynamic Content

There may be a possibility that we have to apply wait for any element to be loaded in the DOM before the test procedure can be carried forward. Timeout can be classified in two ways:

Strict Timeout: You can define timeout in minutes or seconds. For example

Home page test
        wait 10s
        check homepage.gspec

Condition Based Timeout: For this way of waiting you need to provide a locator (css, xpath or id) for an element and a condition for it. There are 4 conditions that could be used in wait action:

  • element appears in DOM
  • element is removed from DOM
  • element becomes visible
  • element gets hidden

In case the condition fails, Galen will throw an exception and interrupt the test. For example:

@@ groups Business_Section
Checking the responsiveness for business section in ${browser} browser on
  selenium ${browser} HTTP://${domain}/business ${size}
  wait 10s until exist "css: div#nebula_div_btn"
  check ././Specs/Cross_Specs/CGU_Business.gspec --include "${tags}"

Would love to know if you have any further thoughts or insights on Galen, or about this Galen framework tutorial. Just drop a line the comments below and we can start a discussion.

Shared Success

Building a Consent Management Platform for Compliance and Protection of PII Data
How Launching a Dynamic eCommerce Platform Streamlined Procurement for the Dental Support Organizations
Building Enterprise Chatbots With Amazon Lex
Case Study on India Today Network: B2B Classifieds Portal

Let’s start our conversation

  • Business Inquiry
  • Career
  • Others

Business Inquiry