While good testing and version control habits are always helpful and save a lot of time, the process of committing changes, running tests, and deploying the changes can in itself be time consuming. This is especially true in an agile development process, which aims to make small, incremental changes in a series of sprints. Ideally, the process of committing, testing and delivering could be done in a single command.

This is where CI/CD comes in. An Oracle blog post on CI/CD describes the software development pipeline as being a four-step process: commit, build, automated tests, and deploy. CI/CD involves automating this process so that a single commit results in changes deployed to production, so long as the changes can be built and pass the tests. However, any of these stages can be skipped and not all of them have to be automated if it doesn’t make sense to do so. Additionally, other stages can be added if desired.

Oracle stresses the importance of testing in this process, and the requirement to have a suite of unit, integration, and systems tests. These are important to have for any project, but are vital if a commit is automatically deployed to production to make sure users are getting a reliable product.

Gitlab uses Runners to run the jobs defined in a file named “.gitlab-ci.yml”. Jobs can be defined in the stages mentioned above, or any arbitrary number of custom stages, to create a single pipeline. When a commit is made, the pipeline lists the stages and whether they pass. Of course, unit tests should be run before a commit to ensure that the code is behaving as expected, but once a change is committed the rest of pipeline can be automatic.

In large systems, this automation is especially useful. You may be not able to compile an entire code base on a local machine. You may not be working on the same schedule as the rest of your team. Automating other portions of testing and deployment allows a single developer to finish a feature or patch on their own and reliably get it into the hands of users.

In researching software engineering jobs, it seems that many companies use Docker as part of their CI/CD process. Imagine you want to make sure your software runs on Mac and Windows machines. Docker can use predefined images to build isolated containers in which the code can be run. A pipeline can contain separate build stages, for example, to make sure the code builds on both operating systems before running tests and deploying. Next week, I will look at Docker in more detail and describe how it can be applied to software testing.

From the blog CS@Worcester – Inquiries and Queries by ausausdauer and used with permission of the author. All other rights reserved by the author.

SOLID is an acronym for a set of important design principles. Paired together they create a framework for worry free code, and by “worry free” I am speaking of code that would trouble you if any changes needed to be made. In the world today things are constantly changing and being updated and so should your code. If that’s the case then any code you write should have the ability to be edited without causing a complete overhaul of your whole program. Basically what you want to avoid is trickle down effects, and unlike trickle down economics, this is real. If you change one thing or responsibility of a class or variable and that causes a cascade of continuous changes and troubles, then you are experiencing this trickle down effect. To help with this issue is the first design principle in the acronym, Single Responsibility Principle.

Single Responsibility Principle is exactly what it sounds like. Give your classes and methods a sole responsibility so that if they are changed it will only effect that method or classes responsibility. If a class or method handles multiple responsibilities then changing the design of one part may be cause to change the entire entity. 

A crude example would be a Rectangle Class. Let us say you have a constructor to build a rectangle object and all it does is take arguments for height and width. However, you also add if and else statements in the constructor to see if the dimensions make a square and printing a confirmation message if it is. Perhaps you even write “if (myShape.isSquare())..” to send the object to a method to, but this is giving the constructor more than one responsibility. If you decide to change the placement of the square check then there will either be duplicated code or you will have to edit the constructor to pass the isSquare result to other methods. Doing any of this would result is test case changes if you were testing the code. In this scenario it is best to have the constructor just be the constructor and to dedicate the square check to its own method like isSquare. In this case if changes were made then only a single class would require changes and not several that are connected in a convoluted fashion.

I think the Single Responsibility Principle is a must know. I remember beginning coding is CS140 and Data Structures and I would try to get as much done in as few methods as possible by cramming in multiple functions into them. I thought the less methods the better but I was so wrong, it’s worth so much more to have many separate methods and classes that each have a sole function. This way code is organized, easy to arrange, and simple to implement or change.

SOLID Design Principles Explained: The Single Responsibility Principle. (2018, December 17). Retrieved from https://stackify.com/solid-design-principles/

From the blog cs@worcester – Zac's Blog by zloureiro and used with permission of the author. All other rights reserved by the author.

There are many design patterns that assist in building software architecture. They fall into four categories: creational; structural; behavioral; and concurrency. Each of these groups has many specific design patterns, but to focus on more than a single pattern in a blog post would be remiss.

The Coding Blocks Podcast has a series on design patterns, the first of which discusses creational patterns, which are described in the “Gang of Four” book, “Design Patterns” [1]. While the hosts find the overuse of these design patterns humorous, they admit that seeing the word “Factory” instantly describes code at a higher level. Furthermore, design patterns assist in adhering to other object-oriented design principles.

[Design Patterns] help make a system independent of how its objects are created, composed, and represented. 

– Design Patterns, Gamma, E., et al

I have come to strongly dislike nested if statements, checking if a subclass is an instance of a superclass, and switch statements. Clean Code by Robert Martin [2] has influenced that a lot, because it made me realize there’s a better way.

Imagine an app that asks the user what kind of Car they would like. This car needs to drive(), brake(), and calculateFuelCost(). Assume there are dozens of types of Car, each implementing the Car interface with these methods. The app will need a bloated switch statement to make all of these concrete classes, depending on user input.

The idea behind the Factory design pattern is that there is a separate class that creates concrete objects, but returns an abstraction (an abstract class or interface). You don’t need to scatter logic across an application that determines which type of “Car” should be created, for example. In fact, you don’t even need or want to know what kind of car it is, once it’s created. A CarFactory class returns an Abstract Car or a Car Interface. In the case of an interface, concrete classes such as ElectricCar or HybridCar implement the Car interface.

The result is an application that can create a CarFactory, tell it what kind of car the user wants, and then manipulate the returned interface as needed. And no matter the concrete object it gets back, it can be treated the same. This separates the application logic from specific implementation of concrete Car classes.

So when your application needs to add a FlyingCar option, a concrete class can be created that implements the same Car interface. The application only needs to tell the CarFactory to create a new FlyingCar object. The rest can be treated identically, because the CarFactory returns an interface with all the required methods.

As stated in the podcast episode, if this is confusing it means you’re learning. These patterns are not trivial to learn, and require many more examples and plenty of UML diagrams to fully understand the idea behind the pattern.

[1] Gamma, E., et al. Design Patterns:Elements of Reusable Object-Oriented Software. Addison-Wesley, 1995.
[2] Martin, Robert C., et al. Clean Code: a Handbook of Agile Software Craftsmanship. Prentice Hall, 2016.

From the blog CS@Worcester – Inquiries and Queries by ausausdauer and used with permission of the author. All other rights reserved by the author.