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The context plays an important role in how we devise test cases. For example, devising test cases for a mobile app is very different from devising test cases for a web application or software used in a rocket. In other words, testing is context-dependent. Most of this book tries to be agnostic about context. The…

As Dijkstra used to say, “Program testing can be used to show the presence of bugs, but never to show their absence.” In other words, while we may find more bugs by simply testing more, our test suites, however large they may be, will never ensure that the software system is 100% bug-free. They will…

As I said earlier, given that exhaustive testing is impossible, software testers have to prioritize the tests they perform. When prioritizing test cases, note that bugs are not uniformly distributed. Empirically, our community has observed that some components present more bugs than others. For example, a Payment module may require more rigorous testing than a Marketing module. As a…

There is no silver bullet in software testing. In other words, there is no single testing technique that you can always apply to find all possible bugs. Different testing techniques help reveal different bugs. If you use only a single technique, you may find all the bugs you can with that technique and no more.…

Prioritizing which tests to engineer is difficult. Creating too few tests may leave us with a software system that does not behave as intended (that is, it’s full of bugs). On the other hand, creating test after test without proper consideration can lead to ineffective tests (and cost time and money). As I said before,…

We do not have the resources to completely test our programs. Testing all possible situations in a software system might be impossible even if we had unlimited resources. Imagine a software system with “only” 300 different flags or configuration settings (such as the Linux operating system). Each flag can be set to true or false…

A simplistic view of software testing is that if we want our systems to be well tested, we must keep adding tests until we have enough. I wish it were that simple. Ensuring that programs have no bugs is virtually impossible, and developers should understand why that is the case. In this section, I discuss…

Automation is key for an effective testing process. Every test case we devise here is later automated via a testing framework such as JUnit. Let me clearly distinguish between test case design and test case execution. Once a test case is written, a framework runs it and shows reports, failures, and so on. This is all that these…

I have been using two words to describe how I expect a developer to test: effectively and systematically. Being effective means we focus on writing the right tests. Software testing is all about trade-offs. Testers want to maximize the number of bugs they find while minimizing the effort required to find the bugs. How do we achieve this? By knowing…

You may be thinking that forcing developers to apply rigorous testing may be too costly. Figure 1.4 shows the many techniques developers have to apply if they follow the flow I am proposing. It is true: testing software properly is more work than not doing so. Let me convince you why it is worth it: