End-to-end testing is a software testing technique that verifies the functionality and performance of an entire software application from start to finish by simulating real-world user scenarios and replicating live data. Its objective is to identify bugs that arise when all components are integrated, ensuring that the application delivers the expected output as a unified entity.

End-to-end testing is also referred to as E2E testing. Thanks to end-to-end testing, testers gain insights into how the application functions from the end user’s perspective, giving them a more comprehensive understanding the software quality before release.

Importance of End-to-end Testing

End-to-end testing is essential as modern software has grown to be intricate with dozens of systems interacting with each other simultaneously.

Even if these components function perfectly fine individually, they may still fail when integrated due to the miscommunication between components. End to end testing is there to verify the flow of information through the AUT, including all possible paths and dependencies. If there is an issue in any “touchpoint” between software components and/or subsystems, testers can easily locate the root cause and troubleshoot immediately.

Testers would want to achieve the highest level of coverage with E2E testing. All subsystems or components of the application, such as the user interface, application server, database, as well as any external systems that the application may interact with, should undergo E2E testing.

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End-to-End Testing Examples

Here's an example of end-to-end testing for an eCommerce website.

In this scenario, a customer purchases a product from the website, pays for it, and receives a confirmation email. The following tests must be performed to ensure that the feature functions as expected:

Verify the functions of the product page and product selection features
Data validation feature in the customer information form
Payment information validation
Verify the payment processing feature
Verify that the payment is successful and the website displays a confirmation message.
Check the customer's email inbox for a confirmation email.
Verify that the confirmation email contains the correct details of the purchase (e.g., product name, quantity, price, order number).
Check the customer's account on the website and verify that the purchase is listed in the order history.

Here we are validating the entire purchasing process, from selecting a product to receiving a confirmation email. We also check that the website components (shopping cart, payment system, email notification) are all smoothly interacting with each other.

Benefits of End-to-End Testing

End-to-end testing has been more reliable and widely adopted because of the following benefits:

Quality management across multiple application levels: modern applications are built upon complex architecture consisting of multiple layers with interconnected workflow. These layers may work fine individually but conflict with each other once connected. E2E testing can verify the interactions between these individual layers and components.
Backend QA: E2E testing first verifies the backend layers, especially the database of the application, which feeds critical information to other layers for the application to work.
Ensure consistent application quality across environments: E2E testing verifies the frontend, ensuring that the application works as intended across a wide range of browsers, devices, and platforms. Cross-browser testing is frequently performed for this purpose.
Third-party applications testing: there are external systems integrated into the application to perform highly specific tasks. End to end testing ensures the compatibility between external and internal systems, as well as the data communication between them.

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End-to-End Testing Lifecycle

An end-to-end software testing life cycle consists of four components: Test planning, Test design, Test execution, and Results analysis.

Test Planning: This phase takes place when integration testing is complete. In a test plan, test objectives are outlined based on the initial client requirements and application architecture.
Test design: A proper test environment is set up based on the requirements. Usually the test environment is already configured for previous test runs, and testers can leverage these existing configs. Risk analysis and usage analysis is also conducted to more effectively allocate the suitable resources to achieve test objectives. After that, testers start creating the necessary test cases, utilizing automation testing tools to minimize time spent on test design
Test execution: Test cases are executed, locally and remotely. Monitor test progress for consistency with the original test plan
Results analysis: Analyzes test results and pinpoint the root cause of the bug. These discoveries will be sent to the development team for immediate intervention. Then a project retrospective is implemented to evaluate processes and discuss areas of improvements.

Types of End-to-End Testing

Horizontal E2E test

Horizontal end to end testing is what the end user thinks of when they hear “end-to-end testing”. In this approach, testers focus on ensuring that each individual workflow in the application works correctly.

The eCommerce example above is exactly what horizontal E2E testing looks like from the end user’s perspective. The tests to be performed involve verifying the Product Search feature, the Product Page functionalities, Product Ordering steps, and Shipping details.

In other words, with horizontal end-to-end testing, QA professionals want to put themselves in the position of the user and test how they experience every customer-facing aspect of the application.

Vertical E2E test

Vertical E2E testing is a more technical approach. This is what the tester thinks when they hear end-to-end testing. Unlike end users who only experience the frontend, testers also work with the backend, and they want to make sure that the right data is transferred to the right place, at the right time, so that all background processes keeping the application running can be smoothly executed.

In the eCommerce website context, vertical E2E testing involves verifying the Account Registration & Verification process, account-related features, the product database, product updates, and eventually the UI (frontend). These vertical E2E tests happen in sequential, hierarchical order.

End-to-End Testing Success Metrics

Some of the many testing metrics used for E2E testing include:

Test Case Preparation Status: Used to determine the specific position of the test cases that are under preparation, compared to planned test cases.
Test Progress Tracking: Test progress should be tracked on a weekly basis. This step provides regular details of test completion percentage, such as passed/failed, executed/unexecuted, valid/invalid test cases, and so on.
Defects Status and Details: It gives a weekly percentage of open and closed defects. Also, weekly defect distributions are based on severity and priority.
Environment Availability: The actual number of operational hours and hours scheduled per day for testing.

End-to-end Testing vs Functional Testing

End-to-end tests are not just several unit tests and functional tests strung together – they are more complex and carry more risks. We’ve listed the main differences between functional and E2E tests to illustrate this further.

Aspect	Functional Tests	End-to-End Tests
Scope	Testing is limited to one single piece of code or application.	Testing crosses multiple applications and user groups.
Goal	Ensures the tested software meets acceptance criteria.	Ensures a process continues to work after changes are made.
Test Method	Tests the way a single user engages with the application.	Tests the way multiple users work across applications.
What To Validate	Validate the result of each test for inputs and outputs.	Validate that each step in the process is completed.

End-to-End Testing vs Integration Testing

End to end testing is quite similar to integration testing, and indeed they do overlap in several aspects. Here are some major differences between them:

Aspect	Integration Testing	End-to-End Testing
Perspective	Technical team’s point of view	Final user’s point of view
Goal	Ensure that application components work together	Ensure that the User Experience is consistent
Scope	Multiple components within in one applications	The scope may span across the entire technology stack of the application
Cost	Less expensive to implement	More expensive to implement due to the hardware - software needed to best simulate real-world scenarios
Time needed	Faster than E2E testing (about less than 1 hour for 200 tests)	Longer than Integration testing (may take up to 4 - 8 hours)

End-to-End Testing Main Challenges

Detecting bugs in complex workflows certainly has its challenges.

1. End-to-end testing can be time-consuming

Creating the necessary test suites and matching them to the user’s navigation within the application may require the running of thousands of tests and can be quite time-consuming. Usually QA teams leverage automation testing tools to assist them in such tasks. These tools should give testers the collaboration capability so that they can align with the development teams on what to test.

2. Setting up the right test environment

Accessing a proper test environment is not always straightforward and can include having to install local agents and logging into virtual machines. To reduce the difficulties, it is better to adopt an on-cloud testing system which gives testers access to a wider range of platforms and environments to execute their tests on, saving the initial investment into physical machines.

End-to-End Testing Best Practices

1. Focus on your application’s critical workflows first

It's important to prioritize critical parts of the application. Focus on what most people use in your application and create tests for that in advance.

After selecting the most critical workflows, start by breaking them down into smaller steps. This gives you a more focused perspective into how your tests should be carried out and minimizes the number of unrelated tests.

2. Avoid exception testing

Exception testing is the process of testing the behavior or system when it encounters an error condition or exceptional event. Although it is a highly recommended practice, end to end testing is not suitable for exception testing. This type of test may identify that an error occurred but does not necessarily tell us why the error happened or how it will affect the application or system.

3. Build End-to-End tests that minimize UI flakiness

When it comes to end-to-end tests, UI tests are usually involved, and these types of test regularly fail due to the flaky nature of interacting with the system from the perspective of the end user. Network issues, server slowness, and many other aspects can affect the test results and generate false positives.

To deal with such flakiness, it is recommended to account for unexpected system issues while performing your tests. For example, with Katalon, testers can utilize the Smart Wait feature to wait until all elements on the screen have been loaded before continuing the predefined actions.

4. Leverage automation testing

Unlike other types of testing, end-to-end testing involves testing the application's functionality from end-to-end, covering all possible user scenarios, interactions, and interfaces. It requires a higher level of coordination and collaboration between teams, as it involves testing the integration of various modules, APIs, and systems.

For end to end testing, we need more than just test automation tools. We need a software quality management platform. Such a platform provides a comprehensive test management system that allows testers to manage and organize test cases, requirements, test plans, and defects in a single place.

End-to-End Test Automation with Katalon Studio

Katalon logo

Katalon is an excellent software quality management platform that can make your end-to-end tests less complicated. With Katalon, software teams can have an end-to-end perspective of their testing activities, from collaboration for test planning, test authoring, test execution, test artifact management, to test analytics and reporting.

Katalon supports a wide range of testing types, and both developers and manual testers can easily automate UI or functional testing for web, API, desktop, and mobile applications, all in 1 place. Tools used across the software testing life cycle can natively integrate with Katalon, giving you a comprehensive testing experience. (your existing CI/CD pipeline and test management tools).

Katalon has several noticeable features to support your E2E testing activities:

1. On-cloud Test Execution

Performing end-to-end testing across multiple browsers and operating systems can be a daunting task, especially when it comes to setting up physical machines to execute tests. This process can be time-consuming and resource-intensive, leading to delays in the end-to-end testing process.

By leveraging Katalon, you can easily run tests on the cloud, on a wide range of multiple browsers, devices, and operating systems simultaneously, ensuring comprehensive test coverage. This feature helps organizations save time and resources while improving the quality of their web applications.

2. Katalon Recorder

Different use cases are often mixed together in different orders and variations. But we can call each grouping of use cases a user journey. Technically, a user journey is a collection of steps in which each step corresponds to a user action. Collectively, they represent a typical user session.

Katalon offers the Recorder feature on the web to help you accomplish the task of creating user journeys without any hassle. The Recorder essentially watches and records all your movements on the application so that you can focus on creating the journey itself.

3. Built-in keywords

built-in keywords in Katalon Studio for keyword-driven testing

A user journey usually consists of hundreds of steps. When a test case – which represents a user journey – fails, it may be easy to pinpoint superficial causes (e.g. a change in a Web element’s property). However, it is harder to diagnose the actual cause solely based on the fact that the test has failed. It could have been because the current page is not the same page that was recorded because at some points the test case went off the right track.

To ensure that the user journey has to go through certain milestones, test oracles are necessary. Test oracle refers to a mechanism to ensure that the test case is being executed as expected. In Katalon, a set of built-in keywords that implement this concept is provided. You can assert or verify a web element against certain text that you expect it to contain, or its properties against some expected properties and many other types of expectations.

4. Custom keywords

Depending on the business logic of your application, there may be behaviors that occur across different pages but differ only in some known characteristics. In such cases, it is a best practice to capture these behaviors in a behavior template that can be filled with specific information when necessary.

In Katalon, a custom keyword can be defined to represent such a behavior template. Once defined, it can be reused in different test cases and even in different test projects. You can even share your custom keyword as a plug-in through Katalon Store so that others can benefit from it.