The potential benefits of containerization are being discovered across the breadth and the length of software engineering. Previously, testing sophisticated software systems involved a number of expensive and hard-to-manage server modules and clusters. Considering the costs and complexities involved, most of the software testing is accomplished using mocking procedures and stubs. All of this is going to end for good with the maturity of the Docker technology. The openness and flexibility of Docker enable it to work seamlessly with other technologies to substantially reduce the testing time and complexity.

For a long time, the leading ways of testing software systems included mocking, dependency, injection, and so on. Usually, these mandate creating many sophisticated abstractions in the code. The current practice for developing and running test cases against an application is actually done on stubs rather than on the full application. This means that, with a containerized workflow, it is very much possible to test against real application containers with all the dependencies. The contributions of the Docker paradigm, especially for the testing phenomenon and phase are therefore being carefully expounded and recorded in the recent past. Precisely speaking, the field of software engineering is moving towards smarter and sunnier days with all the innovations in the Docker space.

In this chapter, we clearly expounded and explained a powerful testing framework for integrated applications using the Docker-inspired containerization paradigm. Increasingly, for the agile world, the proven and potential TDD method is being insisted as an efficient software building and sustenance methodology. This chapter has utilized the Python unit test framework to illustrate how the TDD methodology is a pioneering tool for software engineering. The unit test framework is tweaked to be efficiently and elegantly containerized, and the Docker container is seamlessly integrated with Jenkins, which is a modern day deployment tool for continuous delivery, and is part and parcel of the agile programming world, as described in this chapter. The Docker container source code is pre-checked before it enters into the GitHub code repository. The Jenkins tool downloads the code from GitHub and runs the test inside a container. In the next chapter, we will dive deep into and describe the theoretical aspects of the process isolation through the container technology and various debugging tools and techniques.