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Integration Testing vs End-to-End Testing

Integration and end-to-end testing are distinct methods QA teams use during various application development stages. Unit testing is the primary focus during the early development phase. As multiple components are created, testing shifts to integration scenarios. The next, arguably most crucial stage is end-to-end testing, which becomes the primary focus. Let’s take a closer look at integration and end-to-end testing.

Integration Testing

A software application comprises different components. So integration testing focuses on how these various components interact and work harmoniously. When one component has functionality dependent on another component, integration testing is carried out to test these functional dependencies. Integration helps to validate the data flow between two modules. The testing will be carried out in a local or staging environment.

Consider an application with an accounting platform that takes care of the user logging in and creating session IDs. Similarly, we have a cart platform where users can add an item to the cart only if logged in. So the cart platform has a dependency on the accounting platform to validate session ids. When performing integration testing, the primary focus will be testing the session ids, and test cases will be based on session id functionality.

There are three approaches to integration testing:
  • The Bottom-Up Approach
  • The Top-Down Approach
  • The Big Bang Approach

The Bottom-Up Approach

Bottom-up integration testing is done by first integrating and testing low-level modules, then testing the high-level modules. High-level modules are simulated or mocked to test the low-level modules; these simulated modules are called drivers. The main advantage of bottom-up testing is a higher success rate, since the low-level modules are tested first. Finding defects in low-level components is easier and can be fixed right away.

The only disadvantage in this module will be the high-level modules which are more critical, will be tested at the last stage. This approach can also be called inductive reasoning.

The Top-Down Approach

The top-down approach (surprise, surprise!) is the reverse of the bottom-down approach. The high-level modules are combined and tested initially, and then the low-level components are tested. If there is any dependency on low-level modules initially, it will be mocked. These mocked systems are called stubs. The high-level modules are tested first, so that any critical functional issues will be captured and fixed earlier.

Because the low-level module is simulated, it requires creating a lot of stubs for testing, and the lower-level modules won’t be tested thoroughly. The advantage of using this method? QA team can capture integration errors earlier.

The Big-Bang Approach

In this approach, all the modules are integrated and tested as a single unit. So the integration happens all at once instead of one after the other. This approach is used only if the application is small or has a tight deadline. The major drawback of this approach will be that if there is any issue, it will be challenging to find the root cause module. Also, the integration can be performed when all the components are developed, so their allotted time for testing will be significantly less. The crucial integrations cannot be adequately tested, leading to defect leakage.

End-to-End Testing

End-to-End (or E2E) testing verifies if the application behaves according to the requirements. It validates the entire user flows. E2E testing typically happens in a production-like environment simulating real-world situations, test data, and infrastructure. The testing won’t focus on the functionality of any components; instead, it will focus on use cases that will start from the initial step till the end of the flow. Each use case is intended for different workflows of various lengths and complexity.

End-to-end testing can be approached in two ways:

  • Horizontal End-to-End testing
  • Vertical End-to-End testing

Horizontal End-to-End Testing

Horizontal E2E confirms if the intended user can navigate across the application without any issues. The entire workflow is thoroughly tested. For example, in horizontal testing, the testing can start with creating an account, searching for items, adding them to the cart, checking out, making payment, selecting the delivery option, and placing an order. So here, the user navigates across the application. The QA team can capture any failures or changes from the requirements on the go. One of the significant advantages of doing horizontal E2E is to get precise user experience testing. Horizontal E2E can be considered as a final step in release cycle testing.

Vertical End-to-End testing

Vertical E2E is more granular compared to horizontal E2E. In Vertical E2E, testing is carried out in different layers, such as the database, API, or UI layer. For example, if the UI part is not ready, but all the API components are, then the QA team can start E2E testing on the API layer. The advantage of this testing type is that the bugs in user flows can be captured early – since the testing happens separately for each layer. It’s straightforward to distinguish which layer has the bugs. On the contrary, finding out when the user does a horizontal E2E will be challenging.

Integration vs. End-to-End

When comparing integration and end-to-end testing, we must remember that both tests come in different areas of the software life cycle, and they pursue different goals.

Integration Testing End-to-End Testing
Performed when multiple components are ready. Performed at the end stages of application development.
Testing takes significantly less time since tests typically include less steps – as it’s based on the
functionality of a particular component.
Testing takes a longer time since most of the scenarios are end-to-end.
Stubs and drivers are used for testing, making it less realistic. Testing happens in a staging (production-like) environment.
Testing starts at the early stages. Testing occurs close to the release or deployment stage.
Focuses on testing how multiple application components interact with each other. Focuses on testing the user experience end-to-end.

Testing is always a time-bound operation. The sooner you’re able to get the test results and identify bugs, the better – which is why test automation is becoming a crucial part of any modern software team.

And while most people think that setting up a test framework and writing good automated tests is extremely complicated, it’s not the case anymore with tools such as testRigor. The reality is that any team can seamlessly build both integration and end-to-end tests using only plain English, without any coding knowledge at all. But don’t think of it as a basic alternative to more mature tools – in fact, it’s exactly the opposite. You can seamlessly create cross-browser and cross-platform tools for web, mobile, and desktop. And it doesn’t stop there – since there’s also support for visual testing, email testing, SMS and phone call verification, 2FA testing, and so on. Don’t just take our word for it – try testRigor yourself for free and see how it can truly bring your QA processes to the next level.

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