In a modern software, dependency is high. Everything’s connected, from microservices, APIs, frontend logic, to third-party tools, and you need to test the flow from start to finish to make all those parts work well together. That’s where end-to-end testing comes in.
End-to-end testing (or E2E testing) simulates real user journeys across your entire app to make sure every part of the system works together exactly as it should.
What is end-to-end testing?
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.
Benefits 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.
Example of end-to-end testing
Let’s take an example of an e-commerce website to understand E2E testing.
End-to-end testing here means testing all parts of the system, including the frontend, backend, database, and third-party services (payment, email), work smoothly together. The full workflow to test is:
- Open Website
- Search for Product
- Select Product
- Add to Cart
- Checkout
- Enter Payment Details
- Place Order
- Receive Confirmation
- Admin Checks Order
- Track Order
When to do end-to-end tests?
Due to its scope, end-to-end test is usually done at the end of the process. Let's look at the test pyramid to see why:
A comprehensive test strategy should include 3 layers of tests:
- Unit tests (base of the pyramid): These tests focus on individual components, like functions or methods, ensuring that each small piece of the system works correctly in isolation.
- Integration tests (middle layer): Once individual components work, it’s time to check if they function properly together. Individual components that passed unit tests can totally break when they are integrated, usually due to data miscommunication. Integration tests ensure that data flows correctly between modules and that interfaces are solid.
- E2E tests/system tests (top of the pyramid): End-to-end tests validate the entire application, from the user interface to the back-end, ensuring the system works as a whole. These tests give high confidence in meeting business requirements, but they’re slower and more complex. Because of this, they should be limited to critical workflows to avoid flakiness.
As you can see, while unit testing is only concerned with ‘Is this specific module working well individually’, integration testing is concerned with ‘Are these modules working well together?’, end-to-end testing is much more comprehensive: 'Is everything working well together?'
In a good test strategy, E2E tests should only account for 5-10% of the total number of tests. This figure is around 15-20% for integration tests and 70-80% for unit tests.
Challenges of end-to-end testing
1. Setup complexity
Setting up E2E tests isn’t trivial. The more third-party services, the harder it gets. When systems depend on multiple microservices, cloud APIs, or external providers, test orchestration becomes fragile and bloated. This is especially painful in production-mirroring environments.
2. Flakiness is sometimes inevitable
Flaky E2E tests are pretty annoying, or worse, they actively damage engineering velocity. Test failures that aren’t actual regressions create noise, undermine trust, and introduce risk fatigue. And, teams often lack the tooling or observability to identify root causes fast enough.
3. Debugging failures is a challenge
Unlike unit or even integration tests, E2E failures are often opaque. Logs are verbose, contexts are shared, and side effects cascade unpredictably. Without precise traceability, a red CI run becomes a forensic investigation.
How a NASA failure proves the importance of E2E testing
The 1999 Mars Climate Orbiter disaster is one of the clearest real-world examples of why end-to-end (E2E) testing matters.
Here's the story: NASA lost a $125 million spacecraft because one team used imperial units (pounds), while another assumed metric units (newtons).
Why did this happen? Because no test ever verified the full journey from data generation to thruster execution. The error slipped through multiple layers because each part worked in isolation, but the system failed as a whole.
That proves the importance of end-to-end testing in ensuring that the system works in concert.
Types of End to End Testing
There are two types of end-to-end testing. They describe how you test your application, either from the user’s perspective (horizontal), or the system’s internal logic and layers (vertical).
1. Horizontal E2E test
Horizontal end to end testing is what the end user thinks of when they think of “end-to-end testing”. In this approach, testers focus on ensuring that each individual workflow in the application works correctly.
With horizontal end-to-end testing, testers want to put themselves in the position of the user and test how they experience every customer-facing aspect of the application.
It focuses on:
- User workflows
- UI interactions
- Entire application flows
In other words, you’re testing the app from the outside in, exactly like a real user would.
2. Vertical E2E test
Vertical E2E testing is a more technical approach.
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.
This one’s less about workflows and more about testing across layers of your system.
It focuses on:
- Backend
- APIs
- Databases
- Integration between services
In other words, you’re testing the depth of one part of the system.
End-to-end testing process
End-to-end testing is done in the same process as any other types of testing:
- 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.
📚 Read More: How To Write a Test Case?
End-to-end testing vs integration testing
Here is a comparison table for the differences between end-to-end testing and integration testing:
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Aspect
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Integration Testing
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End-to-End Testing
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Perspective
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Technical team’s point of view
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Final user’s point of view
|
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Goal
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Ensure that application components work together
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Ensure that the User Experience is consistent
|
|
Scope
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Multiple components within in one applications
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The scope may span across the entire technology stack of the application
|
|
Cost
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Less expensive to implement
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More expensive to implement due to the hardware - software needed to best simulate real-world scenarios
|
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Time needed
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Faster than E2E testing (about less than 1 hour for 200 tests)
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Longer than Integration testing (may take up to 4 - 8 hours)
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📚 Further reading: End-to-end Testing vs Integration Testing
End-to-end Testing vs Functional Testing
Here is a comparison table to illustrate the differences between end-to-end testing vs functional testing:
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Aspect
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Functional Tests
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End-to-End Tests
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Scope
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Testing is limited to one single piece of code or application.
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Testing crosses multiple applications and user groups.
|
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Goal
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Ensures the tested software meets acceptance criteria.
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Ensures a process continues to work after changes are made.
|
|
Test Method
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Tests the way a single user engages with the application.
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Tests the way multiple users work across applications.
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What To Validate
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Validate the result of each test for inputs and outputs.
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Validate that each step in the process is completed.
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End-to-end testing vs System testing
System tests verify a complete, functional area of the application in isolation. It’s about validating a major block of functionality, but not the entire user journey.
End-to-end tests validate the entire flow from start to finish, across multiple systems, layers, or components.
Put simply:
- System tests check complete subsystems behave correctly.
- End-to-end tests check the entire system behaves correctly as a whole, across real-world workflows.
End-to-end testing best practices
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Start with E2E for basic coverage. If your project lacks tests, E2E can be the fastest way to establish guardrails, especially for sanity checks like “does the site load?”, “does the login form work?”, or “can users complete a basic flow?” This is a low-effort way to catch showstoppers early.
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Use E2E to bootstrap testing in legacy codebases. When there are no unit or integration tests, E2E tests often provide the clearest path to coverage without requiring risky refactors. They let you wrap critical paths with protection before going deeper.
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Prefer E2E for API-level checks over UI tests. Testing full user flows through a website can be brittle and hard to maintain. API-focused E2E tests break less, are easier to debug, and give better ROI when validating business logic and cross-service integration.
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Avoid E2E for edge cases and exhaustive testing. Covering all UI corner cases with E2E gets expensive fast. These are better handled with unit and integration tests, which are faster, cheaper to run, and less likely to rot.
Top end-to-end testing tools and frameworks
1. Katalon
Katalon is an excellent software quality management platform that can make your end-to-end tests a breeze.
With Katalon, QA teams can:
- Unify all testing activities (test planning, test authoring, test execution, test artifact management, to test analytics and reporting) in one platform
- Create automation tests for web, mobile, API and execute across a wide range of environment
- Receive AI-powered test case recommendations, generate synthetic test data, create test cases from plain language input, and auto-maintain flaky tests
2. Autify
Autify is a test automation tool designed for web and mobile applications. It allows users to automate E2E tests by recording interactions using its Chrome extension, then execute these tests across multiple platforms, including Windows, Linux, and Mac, as well as various web and mobile browsers. Its key features include:
- Smart Test Automation – Utilizes AI and machine learning to detect UI changes and adapt test cases automatically.
- Visual Test Editor – Enables test creation through a simple drag-and-drop interface.
- Seamless Integrations – Connects with CI/CD tools like CircleCI, Jenkins, and GitLab.
- Comprehensive Test Reporting – Provides detailed analytics, reports, and test execution logs with screenshots and video recordings.
3. testRigor
testRigor makes automated testing easy with simple plain commands, perfect for manual QA testers with little coding experience. Its AI-powered automation boosts test coverage with minimal effort. You can also create custom test cases for complex scenarios.
Key features:
- Simulates real user interactions for accurate testing.
- Codeless cross-platform testing for web, native, and hybrid mobile apps.
- Integrates smoothly with test case management systems.