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What is a Test Runner

By Kitakabee, Community Contributor -

As the name suggests, Test Runner is a tool that is used to run or execute tests and export results. It is a library that selects the source code directory and picks the test files to run them for verifying bugs and errors. The Test Runner also ensures to run the file and lets you know if the test files are executing properly as programmed to meet the benchmark standards. The test runner can run functional tests and writes results according to your setup. 

You can use a test runner either by giving command line arguments or with the help of a ReadyAPI user interface like SoapUI. Today, there are various types of test runners like JUnit test runner, Karma, Python test runner, etc. These can run a single or group of test files automatically when a specific code or script is provided. The basic point to know about test runners is, that they can be executed in Selenium or Appium, based on the nature of the software. 

If the software application is web-based, then a test runner in selenium is used and for mobile based applications, Appium is the best of existing automation tools. Selenium is the open-source tool that lets QAs automate web browsers with the help of Selenium WebDriver, Selenium Grid, and Selenium IDE. It is popularly known for its flexibility and compatibility. It supports most of the benchmark browsers and operating systems and allows you to automate in various programming languages like Java, C#, Python, NodeJS, Ruby, and more. 

To run the tests and identify bugs in the test suite, the Test Runner should be capable of executing test files on multiple real devices for faster and more accurate results. 

BrowserStack can execute Selenium testing at scale by using advanced frameworks like Cypress and others. You can start testing on 3000+ real devices and browsers, execute parallel tests, check the responsiveness of your application without compromising ever on the accuracy and catch bugs before your users do. Head to BrowserStack Automate today to experience a smooth cloud-based test runner with hassle-free parallelization and run your test suite in real user challenges and conditions for the ultimate user satisfaction. 

Try BrowserStack Automate now

Why a Capable and Seamless Test Runner is Important?

Today technology is growing at an unstoppable speed and so is the adaption to the digital sphere. Businesses are constantly trying to excel in providing the best user experience possible through automation, digital infrastructure, and other processes like the agile development models. To run the tests multiple times and check the bugs constantly, takes time and can become tedious. 

Here is where Selenium testing comes to automate the web browsers and test them repeatedly in a quick time allowing you to deliver at speed without any bottlenecks and bugs. Do more in less time and scale faster releases as you go with BrowserStack. Here, you can find both manual testing and automated testing which allows advanced automation without ignoring human importance. 

View the list of Test Runners supported by BrowserStack

Structure of a Test Runner

Test Runners have varied structures. Some of the popular test runner structures are tradefed, Java, SoapUI, etc. 

The tradefed Test Runner includes two types of interfaces – Basic and Advanced.

  • Basic Interface

Here, the tests are executed with an easy and simple ‘run’ method through the IRemoteTestInterface. The IBuildReceiver and IDeviceTest are popular for their wide usage among QA testers and developers. These will aid in the test set-up and provides API to interact. 

  • Advanced interface

For more advanced test runs and interactions between test runner and test harness, ITestFilterReceiver and ITestCollector are the most useful tools. While the former helps in executing test subsets, the latter lets QAs dry-run the tests that aid in accumulating all test cases list. 

The SoapUI ReadyAPI tool includes a test structure classified into three levels such as test suite, test case, and test steps. 

Types of Test Runners

Different types of test runners exist alongside custom test runners. Major test runners like JUnit, GTest, Python, SoapUI, etc, will run your tests in a jiffy and records results in the log files. Let’s look into some of the popular test runners.

  • JUnit Test Runner

To avoid time-consuming testing and executing tests separately, the JUnit framework provides JUnit Core Class method for executing a group of tests along with the main() method. After importing all the necessary namespaces such as JUnit Core, JUnit Result, and JUnit Failure with required command-line arguments, then start writing code in the main ()  method and the full JUnit test runner class looks like the below-given code:

Junit Core Class in main() method

public static void main(String[] args) {

//This will run JunitMathProvider 1 class.

Result result = JUnitCore.runclasses (JunitMathProvider 1. class);

System.out.println(“Total tests count ” + result.getRunCount());

System.out.println(“Failed tests count” + result.getFailureCount());

for(Failure failure : result.getFailures())






Final Code of Junit Test Runner Class

package junits;

import org. junit.runner.JUnit Core;

import org. junit.runner. Result;

import org. junit.runner.notification. Failure;

public class Test Runner {

public static void main(String[ ] args) {

//This result object has many methods which are useful

//Type result and press dot, all the methods will display

//This statement is to load all type of results in the result object

Result result – JUnitCore.runClasses (JunitMathProvider_1.class);

// Here it is getting the run count from the result object

System.out.println(“Total tests count ” + result.getRunCount());

//This is to get the failure count from the result object

System.out.println(“Failed test count ” + result.getFailureCount());

for(Fallure failure result.getFailures())


//This will print message only in case of failure



//This will print the overall test result in boolean type

System.out.println(result. Was Successful());



Here, the JUnit Core Class is used to run the above classes

The test class titled ‘JUnit Math Provider_1’ is used here.

To run the above class, the below command statement is used here


BrowserStack’s Real Device Cloud for Test Runners

Imagine running and executing various test types such as Selenium, Cypress, Puppeteer, and Playwright tests at scale with cross browser testing support like Chrome, Firefox, Edge, etc, in three easy and simple steps.

  • Integrate
  • Run
  • Scale 

This type of test runner with advanced frameworks along with various helpful features like seamless parallelization not only helps to speed up your tests by X fold but also aids agile teams to ship faster with enhanced quality and greater user satisfaction.

However, BrowserStack does not offer a Test Runner. Instead, a real device cloud can be integrated with test automation frameworks and test runners like JUnit, TestNG, etc. Moreover, no matter which test runner or automation suite is selected based on the project requirements. It is necessary to test on real devices and browsers for accurate test results.

Run Selenium Tests for Free 

Difference between Test Runner, Testing Framework, Assertion Library, and Testing Plugin

The different levels of testing software include a test runner, testing framework, assertion library, and a testing plug-in. These different levels of software or abstraction involved in testing suites or stacks are designed to fulfil a specific purpose. Here, let’s look into the difference between various above-mentioned terms and try to understand the working of the same. 

Test Runner

‘Karma’ is the best example of a test runner which uses the ‘Mocha’ testing framework to actually run and execute tests. Also for testing browser-based JavaScript code, Karma is a simple test runner and easy to execute tests. While test runners operate on the highest level, the remaining testing software executes within the test runner. Here, for executing test runner configurations a typical file named ‘karma.conf.js’ is created with a ‘karma init’ as the command.

  • Code or Test Runner – Karma:

module.exports = function(config) { config.set( ( basePath: ‘../..’, frameworks: [‘mocha’]

Testing Framework

Mocha is the testing framework used here to plug it into the Karma test runner to start executing the test suites and stacks. Frameworks are there to execute and organize tests. Jasmine is also a testing framework similar to Mocha which works both in browser and Node.js. 

One may get quite confused between the Mocha and Chai assertion library. Remember that these two are different abstraction levels and the ‘it’ block is used as an interface to differentiate between the same. The basic thumb of the rule is, that everything which executes or occurs ‘outside’ the it block is related to the testing framework. Contrarily, the methods that are tested ‘inside the it block are related to the assertion library. As a result of these statements, it can be comprehended that anything that is occurring ‘inside’ the ‘it’ block is executing on a lower abstraction level than the testing framework and can be related to either the assertion library or testing plugin. 

The various methods that are coming from Mocha include beforeEach, describe context, and it. Now the differentiation concept will be easier with the ‘it’ block acting as an interface between Mocha and Chai. 

Code for Testing Framework – Mocha

describe(‘the todo.App, function()


context(‘the todo object’, function(){

it(‘should have all the necessary methods’, function(){

var msg = “method should exist’;

expect(todo.util.trimTodoName, msg).to.exist;

expect (todo.util.isValidTodoName, msg).to.exist;

expect(todo.util.getUniqueId, msg).to.exist;




Assertion Library

Here, you will verify whether the given conditions are valid or not. These are tools that are used to check whether the specific thing is right or not. This is the level where you can easily test your code without the need for giving various commands for if statements. This library executes a variety of specs to determine the correctness of the same.  Mocha is programmed and designed in a way that requires an external assertion library for running the test suites. Mocha is also flexible when compared to other relative frameworks using its own assertion libraries. Chai is a solid example of an assertion library that includes methods like except, equal, and exist. 

Code for Assertion Library – Chai

afterEach(function() {





it(‘should have a signup method’, function() {



Testing Plugin

Sinon is a testing plugin hooked to the Chai library which is capable of providing the chance to create diverse test sets. Stubs, mocks, and fake servers can be created through the Sinon plugin and it also allows you to view what is actually happening under the source code. You can also experience some great features while using Sinon. While doing the automation testing using Selenium, you will come across the Selenium IDE, a Chrome and Firefox plugin or extension which is quick and useful for rapid prototyping. 

Code for Testing Plugin – Sinon

describe (‘API integration’, function(){

var server, setupStub, JSONresponse;

beforeEach(function() {

setupStub = sinon.stub(todo, ‘setup’);

server = sinon.fakeServer.create();


it(‘todo. setup receives an array of todos when todo.init is called’, function (){


afterEach(function() {





That’s everything about test runners and test runner in Selenium in the case of web-based software applications. You can also have a basic idea relating to existing test runners and coding execution. To experience the seamless execution of tests across 3000+ Real Browsers and Devices under real user conditions and catch the bugs early in real-time before your users do, which you don’t want the user to find bugs at any costs, check out and try Selenium testing at scale with cloud-based BrowserStack Automate

Execute repeated testing within a short time and ship products to your potential customers in a jiffy. You can also explore other BrowserStack products such as cross-browser testing, interactive and automated mobile app testing, and automated visual testing which consists of advanced features that can enhance your user’s satisfaction and automation testing by many folds. 

Try BrowserStack Automate now

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