In the previous chapters, you learned about the different types of techniques that are used to help to increase the rate at which you deliver changes to your production environment. If you are already using these techniques in your daily work, you will quickly notice that this is only possible if your work is of sufficient quality. If the quality of your work is not high enough, you will face many outages or issues and your end users will not be happy. To be successful, increasing the rate of change and increasing the quality of your work must go hand in hand. To recognize the quality of your work and to increase it, you first need to know what is meant by quality. This is where testing comes in. Testing is the discipline of reporting about the quality of software.

To introduce the topic of testing, this chapter will start by looking at how the quality of software development can be measured. Next, the topic of functional testing will be explored. First, the testing cone and pyramid will be introduced. These are models that can be used to determine which types of tests are needed and how many of each should be used. After this, the different types of tests will be discussed one by one. You will learn about how they work, what they test, and the benefits and downsides of the different types of tests. Finally, the last section will focus on how all metrics and test results, once generated and collected by your pipelines, can continuously report on the quality of the work of your team and even prevent changes of insufficient quality propagating to your users. All of this will help you to maintain the high quality of your software and enable you to confidently deliver that software quickly and frequently.

The following topics will be covered in this chapter:   

• Defining quality
• Understanding test types
• Executing functional tests
• Executing nonfunctional tests
• Maintaining quality