End-to-end testing and regression testing are two important types of software testing.

In a nutshell, end-to-end testing validates the system from start to finish, while regression testing is a technique of running tests on existing working features to ensure that no new bugs are introduced.

Both end-to-end and regression tests are essential for providing quality, reliability, and stability in any software system. 

Knowing the difference between end-to-end and regression testing is key to successful implementation, so let’s take a closer look to understand when to use each type of test and benefit from their particular features.

What is End To End Testing?

End-to-end testing is an essential part of QA and works by performing a comprehensive test of the entire application, from start to finish, so that we can verify it operates as expected.

This type of testing considers all system dependencies and proves that all integrated components work together harmoniously.

E2E testing is designed to verify system integration and data integrity and the goal of an E2E functional test is to efficiently verify that the software components required for a given problem are incorporated correctly.

It is also good practice to closely monitor all subsystems of software for potential failures. Luckily, we can reduce this risk with proper end-to-end testing.

E2E Testing Methods

E2E testing involves testing the application from start to finish, starting from the user's interaction with the front-end interface and continuing through the back-end processes and data manipulation.

There are two main methods of End-to-End testing:

• Horizontal Testing

• Vertical Testing
  

Horizontal testing involves holistically testing the application, while vertical testing examines each system's components separately.

Both methods aid in the recording of system level bugs that will need to be fixed before release.

Horizontal Testing

Horizontal testing is a type of software testing that examines the functionality of an application across various layers of its architecture.

This type of testing is often used to ensure that the application works as expected in different environments, platforms, and configurations.

The goal of horizontal testing is to provide comprehensive coverage of the application’s functionality and to identify any issues that might arise from exploring different user scenarios.

Let's consider an example of an e-commerce website. Suppose a tester wants to test the payment gateway component of the website. A tester can perform horizontal testing by testing the payment gateway component independently. He can check if the payment gateway is working as expected by simulating various payment scenarios and verifying the transaction details.

Vertical Testing

Vertical testing focuses on verifying the functionality and scalability of applications within a particular layer of the technology stack.

This variation of e2e testing is typically used to confirm that applications can handle the expected load in terms of traffic and data.

It helps to identify bottlenecks or issues that may arise due to an increase in the number of users or data.

Vertical testing including performance testing can identify potential performance issues when new features are added.

Now for the same e-commerce website, let's consider the entire flow of the website. A tester can perform vertical testing by testing the entire flow, from login to payment and confirmation. He can start by logging in to the website, adding items to the shopping cart, and then proceed to payment. Tester can verify the payment details and check if the confirmation page appears correctly.

Advantages over other testing methods.

End-to-End testing offers significant advantages as it looks at the system from a more holistic perspective, considering all components.

It provides test coverage at all levels, from UI to the underlying components and back-end systems.

End-to-end testing helps testers pinpoint potential issues in the overall system instead of just individual components.

Moreover, this approach can uncover conflicts between components that might not be detected with other types of testing.

Important factors of E2E

• Automating specific user journeys can enable release teams to reduce the time it takes for their products and services to reach the market.

• Compared to unit and functional testing, e2e makes use of more specific test cases, broadening the scope of the test phase. This, in turn, helps teams boost their test coverage above what they would have been able to achieve using other smaller scale testing techniques.

• It has an important role in the development process, as it reduces the time spent on software testing and minimises the cost of building and supporting software applications.

• The test cases are run according to the end user’s behaviour to validate the proper functionality of the application.

• Assists in steadily and reliably identifying real system level problems.

• Subsystem issues are also identified and rectified, thus enhancing the effectiveness and functionality of the entire system.

Challenges in End-to-End testing

E2E testing comes with its own set of challenges, including:

Test Environment Complexity: E2E tests require a replica of the production environment, which can be complex to set up and maintain.

Test Data Management: E2E tests require large amounts of test data that must be managed, stored and manipulated effectively.

Test Maintenance: E2E tests can become fragile and break easily when changes are made to the system. This requires frequent maintenance, making it a time-consuming process.

Test Execution Time: E2E tests can take a long time to run, especially if they involve a lot of execution steps and system verifications.

Test Dependencies: E2E tests can have many dependencies on external systems, making it challenging to set up and manage test environments.

Test Flakiness: Lengthy automated E2E tests can sometimes be flaky, meaning they may produce different results when run multiple times. This can make it difficult to identify the root cause of the problem when tests fail.

Test Scalability: E2E tests can become complex and difficult to scale as the size and complexity of the system increases.

In conclusion, E2E testing is a crucial part of the testing process. Still, it requires careful planning, design, and execution to overcome these challenges and ensure the system is thoroughly and effectively tested and verified.

What is Regression Testing?

Regression testing is an effective way to check that we don't introduce new bugs after software modification. By running existing tests again and ascertaining that they pass with the latest changes, we can confidently maintain the quality of our software products. 

The term 'Regression Testing' originates from the concept of regression, referring to reverting to a prior state or condition in software engineering.

Quality Assurance teams employ this type of testing to guarantee the ongoing reliability of software and prevent compatibility issues between new and existing elements.

Regression testing is essential for ensuring the smooth introduction of new features. It gives assurance that the procedural performance and operational capabilities of the software remain consistent.

Regression Testing Variations

Retest-all or Complete Regression Testing

Retest-all regression involves running tests against the entire application to ensure that all the existing functionality is still working as expected.

By examining the application as a whole, any errors or regressions that may have been introduced by changes to the software can be identified. Although this type of testing is not recommended for minor issues or changes, it is worth doing to ensure that any modifications to the application do not cause unintended problems or break existing features.

It is a time-consuming process, as all the system’s components must be tested afresh from scratch, including testing every feature of a given product and reusing all test cases, even in areas or portions where no change has been made or created.

High levels of automated testing can streamline the process for efficiency.

This type of regression testing is significant for maintaining the stability and dependability of a system or application. It is used when there is a significant change to the software's underlying code.

Major organisations use this testing method to meet customer requirements and ensure that their systems and applications work as expected.

Selective, Partial or Risk Based Regression Testing

This technique is used to identify and test a subset of existing functionality that is closely related to or may have been affected by other system changes.

This kind of testing verifies that changes made to the system have not caused unexpected behaviour or broken existing functions.

It verifies that a system still works after changes have been made to it and can be used to test both functional and non-functional requirements.

Selective regression testing is a cost-effective method as it uses a subset of test cases to examine the impacted code, thus saving time and effort from creating a new test case and reducing retesting costs.

Progressive Regression Testing

Progressive Regression Testing is a practical approach to software testing that involves periodically retesting software code to ensure that changes have not caused unintended side effects.

This process seeks to verify the software's correctness, completeness, and quality and ensure that changes have not impacted the existing functionality.

It is an ongoing process that should be conducted throughout the entire software development life cycle. Furthermore, Progressive Regression Testing is particularly beneficial when minor modifications are made to the program requirements, as it allows for the creation of new test cases to account for the changes.

This approach is an invaluable tool for ensuring the reliability and integrity of software.

Unit Regression Testing

Unit regression testing is a vital step in ensuring reliable, bug-free software. It verifies that changes to an individual software unit have not caused unintended effects on other units of code.

This process involves testing the individual components in isolation from one another, typically after a code refactor or update.

It is almost always automated to ensure thorough and rapid testing of the code changes. It is important to note that unit regression testing blocks out any external dependencies throughout the test, using mocked functions instead. It is part of the development cycle more so than the traditional testing phase.

Importance of Regression Testing

Maintaining Software Quality

With good regression testing, the quality of the software remains consistent over time and the system continues to work as expected even after changes have been made.

Detecting Defects

Regression testing helps to detect defects that may have been introduced into the system due to changes or modifications. This helps to ensure that the system continues to function correctly and meet the needs of its users.

Confirming that Changes are Safe

Regression testing helps confirm that changes made to the system are safe and do not impact other parts of the system. This helps to reduce the risk of unintended degradation and ensures that the system remains stable and reliable.

Meeting Compliance Requirements

In regulated industries, regression testing is often required as part of the compliance process to ensure that changes made to the system do not violate any regulations or standards.

Improving Time to Market

Regression testing helps to identify defects early in the development process, reducing the time and resources required to resolve them. This can improve the time to market for the software and lower the development cost.

E2E vs Regression Testing: What is the difference?

Conclusion

In conclusion, end-to-end testing and regression testing are two essential techniques used in software testing.

End-to-end testing verifies the overall functionality and integration of the system, while regression testing focuses on maintaining the stability of previously tested parts of the system.

Both techniques are critical in guaranteeing that the software meets the required standards and performs as intended.

The use of end-to-end testing in conjunction with regression testing provides a comprehensive approach to software testing, thereby increasing confidence in the software's reliability and functionality.

Effective testing strategies should include both end-to-end and regression testing, as well as other testing methods, to secure the software's quality and success.

Although end-to-end testing requires intricate automation to be properly implemented, this does not necessarily outbalance the benefit of it as automation can consume large amounts of time and effort for upkeep.

In the digital business world, the amount and complexity of processes are constantly increasing and as so, a well-equipped, modern automated testing tool with all inclusive features can significantly contribute to a successful business outcome.