Testing

"Just as the wise accepts gold after testing it by heating, cutting, and rubbing it, so are my words to be accepted after examining them, but not out of respect for me."

– Buddha

We love this quote by the Buddha. Within the software world, it translates perfectly into the healthy habit of never trusting code just because someone smart wrote it or because it's been working fine for a long time. If it has not been tested, code is not to be trusted.

Why are tests so important? Well, for one, they give you predictability. Or, at least, they help you achieve high predictability. Unfortunately, there is always some bug that sneaks into the code. But we definitely want our code to be as predictable as possible. What we don't want is to have a surprise, in other words, our code behaving in an unpredictable way. Would you be happy to know that the software that checks the sensors of the plane that is taking you on your holiday sometimes...

Testing your application

There are many different kinds of tests, so many, in fact, that companies often have a dedicated department, called quality assurance (QA), made up of individuals who spend their day testing the software the company developers produce.

To start making an initial classification, we can divide tests into two broad categories: white-box and black-box tests.

White-box tests are those that exercise the internals of the code; they inspect it down to a very fine level of detail. On the other hand, black-box tests are those that consider the software under test as if within a box, the internals of which are ignored. Even the technology, or the language used inside the box, is not important for black-box tests. What they do is plug some input into one end of the box and verify the output at the other end—that's it.

There is also an in-between category, called gray-box testing, which involves testing...

Test-driven development

Let's talk briefly about test-driven development (TDD). It is a methodology that was rediscovered by Kent Beck, who wrote Test-Driven Development by Example, Addison Wesley, 2002, which we encourage you to read if you want to learn about the fundamentals of this subject.

TDD is a software development methodology that is based on the continuous repetition of a very short development cycle.

First, the developer writes a test, and makes it run. The test is supposed to check a feature that is not yet part of the code. Maybe it is a new feature to be added, or something to be removed or amended. Running the test will make it fail and, because of this, this phase is called Red.

When the test has failed, the developer writes the minimal amount of code to make it pass. When running the test succeeds, we have the so-called Green phase. In this phase, it is okay to write code that cheats, just to make the...

Summary

In this chapter, we explored the world of testing.

We tried to give you a fairly comprehensive overview of testing, especially unit testing, which is the kind of testing that a developer mostly does. We hope we have succeeded in conveying the message that testing is not something that is perfectly defined and that you can learn from a book. You need to experiment with it a lot before you get comfortable. Of all the efforts a coder must make in terms of study and experimentation, we would say testing is the one that is the most important.

In the next chapter, we're going to explore debugging and profiling, which are techniques that go hand in hand with testing, and are crucial to learn well.

We are aware that we gave you a lot of pointers in this chapter, with no links or directions. This was by choice. As a coder, there won't be a single day at work when you won't have to look something up on a documentation page, in a manual, on a website...