System Testing vs End-to-End Testing: What is the Difference?

System and end-to-end testing are key testing practices in the software development life cycle. However, differences between the two testing practices can sometimes confuse businesses and their quality assurance (QA) teams. We explain each software practice’s benefits, similarities, and differences.   

What is system testing?

System testing verifies a fully integrated and finished piece of software. Through system testing, a QA team assesses how the various application components interact with one another in a complete, integrated system or application. 

System testing falls under black box testing since it examines how the software functions externally from the viewpoint of the user.

In system testing, testers:

When is system testing performed?

Testers often carry out system testing after integration testing and before acceptance testing.

What are the benefits of system testing?

1. Identifying potential problems: System testing can be used to determine program weaknesses and pinpoint areas in need of repair.
2. Ensuring compliance: Testers can determine whether the software meets the program’s criteria and objectives.
3. Complete testing: System testing tests the entire piece of hardware or software, allowing testers to quickly find any flaws or problems that may have slipped through integration and unit testing.
4. Reducing reliance on hard-to-hire technical skills: Testers don’t need additional programming expertise to perform system testing.
5. Accurate testing: The testing environment is similar to the production or business setting.

How is system testing done?

1. Prepare a testing plan: Make a thorough document detailing the testing procedure’s main goals. It’s crucial to develop a detailed guideline so testers can comprehend a project’s scope.
2. Prepare the testing environment: Establish testing conditions suitable for system testing to achieve higher-quality testing.
3. Write test cases: To evaluate a system, create a number of specific test cases for each program feature and employ various system tests.
4. Execute testing protocols: Execute written test cases and test data. 
5. Defect reporting: After the executed testing protocols, defects will be visible to the testers.
6. Regression testing: Testers can execute regression testing finally to examine the side effects of the system testing.

What is end-to-end (E2E) testing?

End-to-end (E2E), also known as chain testing, is methodology for ensuring that software is functioning as intended and that data flow is preserved for all user tasks and processes. 

End-to-end testing aims to simulate a complete production environment by thoroughly testing the entire software for dependencies, data integrity, and communication with other systems, interfaces, and databases. 

It is also a key testing practice when a product is required to function collectively with the other systems in various environments. In such scenarios, validation of data processing from upstream and downstream systems is required to maintain accurate interaction across different platforms & environments.

When is end-to-end (E2E) performed? 

End-to-end (E2E) testing is usually performed after system testing. It is especially useful to identify system dependencies considering that it tests both the software system and the connected systems.

What are the benefits of end-to-end (E2E) testing?

End-to-end testing can provide the following benefits:

1. Increased test coverage: It adds more thorough test cases than other testing techniques like unit and functional testing, which helps teams increase their test coverage. 
2. Reducing overall cost: Decreases the time needed to test software, thereby lowering the overall cost of building and maintaining software.
3. Determining priorities: End-to-end testing assists managers in setting priorities for tasks in the development backlog by determining the significance of a workflow to the user in the real world. 

How is E2E testing done?

Define Test Scenarios

E2E testing begins with defining critical user journeys or workflows that need to be validated, such as user registration, login, checkout processes, or data input and retrieval. These workflows represent the primary ways users interact with the application.

For example, in an e-commerce application, a critical scenario might be verifying the checkout flow from adding a product to the cart to completing a payment.

Set Up the Test Environment

To accurately test an application’s entire flow, the testing environment should mirror the production setup as closely as possible. This may include configuring servers, databases, third-party services, and any other systems or network configurations needed to support the full application.

For instance, in a banking application, setting up the environment might involve configuring test databases, network connections, and external services like payment gateways to simulate the production environment.

Prepare Test Data

E2E tests often require specific data to simulate real-world scenarios. This data can be manually created, imported, or generated through scripts. It should represent realistic use cases that the application will encounter in production.

For example, for a social media platform, sample user profiles, posts, and interactions might be created to represent real user data and actions.

Write Test Scripts

Test scripts are written to automate the actions users would take within the application. Commonly, these scripts are created using E2E testing frameworks like Selenium, Cypress, or Playwright, which provide tools for interacting with the user interface, making API requests, and checking data consistency.

For instance, in a ride-hailing app, automated scripts might include actions like entering a pickup location, selecting a destination, and verifying that a driver is assigned correctly.

Execute Tests

Once the scripts are ready, they are executed in the testing environment. The automated scripts perform each action as a user would, clicking buttons, filling forms, verifying outputs, and checking that data flows correctly between systems.

For example, in a travel booking app, this could involve running scripts that simulate searching for flights, booking tickets, and checking confirmation emails in the test environment.

Validate Results

The final step involves validating the outcomes of each test case against the expected results. This includes checking for correct visual elements, functional responses, data accuracy, and proper integration with third-party services. Any discrepancies are reported as issues.

For example, in a messaging app, validation might involve checking that messages sent by one user appear correctly for the recipient and that notifications are triggered as expected.

Debugging and Re-running Tests

If errors or failures are identified, the code or configuration is adjusted, and the tests are re-run to ensure the issues are resolved. This iteration helps improve the reliability of the application before it’s released to users.

For instance, if a checkout test fails in an online store due to a payment error, the script and payment service would be reviewed, updated, and re-run to confirm the fix.

Methods of software testing 

To understand the positioning of system testing and end-to-end testing, we can look at the three types of software testing.

Black-box

Black-box testing is a software testing method that evaluates the functionality of an application. Knowledge of the internal working structures is not required for this type of testing. It is based on software requirements and primarily concentrates on the input and output of software programs.

White-box

White-box testing examines an application’s internal components or mechanisms in contrast to testing its functionality. Designing test cases for white-box testing involves viewing the system from within.¹ Thus, knowledge of the internal working structure is required for this type of testing. The tester selects inputs to test various code paths and identifies expected results.

Gray-box

Gray box testing is a combination of white box and black box testing. With this method, testers approach the software from an end-user perspective while having partial knowledge of the code internals.

To better understand end-to-end testing, check our article, “7 End-to-End Testing Best Practices”

External Links

• 1. Certification Processes for Safety-Critical and Mission-Critical Aerospace Software - NASA Technical Reports Server (NTRS).