End-to-End Testing: Avoiding Software Failure in Distributed Systems
Nishith Shah April 21, 2021 
Software failures wreak havoc on businesses. Type those words into a search engine and you will get around 93 million results in the blink of an eye. Some of those failures can even be described as epic … and not in a good way.
Yet, because systems are now so complex and interconnected, it can be difficult for companies or stakeholders to understand why an error has occurred. At worst, IT failures can be costly and reputationally damaging. At best, they are a nuisance that detract from the intended customer experience.
Either way, businesses need to root out these failures before they become problems. To put it more simply, it is no longer enough to conduct functional, unit or system testing alone because defects can creep in through the many integrations needed between not only the systems and subsystems but also a host of other means. That’s where end-to-end testing enters the picture.
End-to-end (E2E) testing is a technique which verifies that all the features of a system and its interconnected subsystems work as expected. And in today’s complex, distributed systems where software defects can be very hard to pinpoint, this approach is highly effective at detecting when apps are not performing as they should.
How does end-to-end testing differ from other methods?
More traditional testing methods are limited to validating the performance of a single function, component or application. However, these processes do not account for how the whole system works together as one.
It should be noted that system or integration testing does address this challenge by verifying multiple components are working together as they should. This makes this type of testing useful for improving app performance and reliability but it does not give an accurate picture of how the app is working from the point of view of the end-user.
That is where end-to-end testing comes in.
By simulating the flows that a user would take, E2E testing assesses if end-user performance is functioning as expected. If we take an example of an online purchasing system, say, the E2E testing method would replicate a user logging into their account, adding products to the cart, proceeding towards checkout and filling in the required information to finalize the purchase.
When to perform E2E testing
It goes without saying that E2E tests should be run in conjunction with other testing methods. In fact, they are especially valuable in cases where an output is not as expected, signalling a problem somewhere within the system.
As well as helping to check the overall “health” of an app or product, E2E tests identify errors in the system and its subsystems, validate app behavior over multi-tier architecture and help ensure a bug-free, seamless experience. For more complicated apps, it can be particularly useful in dividing them into multiple tiers for testing.
How to perform E2E testing
Most E2E testing follows this established lifecycle:
- Planning: specify the tests to be run, organize a test schedule and allocate resources.
- Design: take account of the different specifications, requirements and suitable testing frameworks to be used. As part of the design, risk and usage analysis should be considered.
- Execution: run the test cases and document the results.
- Results analysis: check what broke (and fix it), evaluate testing and re-run tests if needed.
There are two ways testing can be conducted – horizontal and vertical E2E testing.
Horizontal E2E testing is the method largely preferred by testers. In horizontal E2E testing, every workflow is tested through a discrete application from beginning to end to check if everything is working as it should.
Vertical E2E testing examines the system in layers and is used for critical modules of a larger, complex system. Testing is conducted in sequential, hierarchical order. In vertical E2E testing, each component of a system or product is tested from start to finish to ensure quality. This kind of testing is mainly used to test critical components of a complex computing system that does not typically involve users or interfaces.
Getting E2E testing right: what are the challenges?
When embarking on E2E testing, the two main trip hazards are issues around orchestration and access.
In E2E testing, the test cases must be executed sequentially. However, it’s not easy to run multiple (sometimes thousands) cases in sequential order in a distributed workflow.
Ensuring continued access can be the other stumbling block. Ensuring continued access can be the other stumbling block. It’s comparatively easier to test custom applications in a virtual test environment. However, E2E testing the actual execution must occur in a production environment and needs a continuous active user session.
When an E2E automated testing bot sets out to test the workflow, it requires local agents to be installed and logged in to remote facilities. The test team will need to find a way to keep the machine awake for the duration of the test and prevent unwanted events interrupting the tests (a Windows update, for example).
E2E testing: why do it?
In a world where digital systems are complex, interconnected and distributed, pinpointing the root cause of a software failure can be akin to finding a needle in a haystack. The problem is that, in this case, the needle has the power to impact customer experience and business performance.
Fixing digital defects requires a holistic approach, and this is where E2E testing can be invaluable. This testing technique tackles two of today’s major digital challenges head on: it helps to improve how end users experience an app as well as identifying the deep-rooted defects in a complex system.
By running E2E testing, software teams can have increased confidence in their software and reduce their time-to-market for new launches. Whether a product already exists or is under development, E2E testing is a valuable tool that decreases repetitive test efforts, mitigates future risks and saves organizations time and money in the long run.
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