These are not really advanced topics, but I wanted to write about them anyway. So here it is.
Sometimes, I report bugs in software. Others, in libraries. Or I can just fix things by myself. And more. Point being: there are lots of bugs everywhere. What do we, software developers, do to avoid writing too many bugs?
We run tests. Unit tests. Integration tests. System tests. Acceptance tests. And where possible, we write software to do these tests for us. Usually, that means unit tests and integration tests. Usually, such tests won’t guarantee that our code is without defect. But at least they give us confidence that it does work for the cases we do tests. If we change something and the tests still pass, we probably have not broken something major. This let us iterate quickly without having to double and triple check whether a change broke one of many features. But even then, starting the tests and waiting for the results is burdensome, so we might get complacent and forget to run them before releasing our changes.
So we get even more software to remember that for us. That’s what we refer to as “continuous integration”, or CI for short. Whenever we submit a new feature, a bugfix, or even if we just want to slightly change the shadow under a button, the CI will run the tests and make sure we have not broken anything. For instance, in the CI of Kepler Project, I run linters to find obvious defects in code, static analyzers to find less obvious defects, as well as a suite of unit tests. I plan to add integration tests at some point, but it is slightly annoying to run them in graphical software.
Once we are confident our changes will not accidentally launch the nukes, we want to actually release them to our users. But software developers are lazy, and they will spend hours automating a task that only takes minutes. In the end, this is the next step after continuous integration, so we call it “continuous delivery” (CD).
An added bonus of a well-designed CD is that you will be able to tell exactly what code was used to create a specific release. For instance, in Kepler Project, the CD starts whenever I create a new git tag. The release it generates uses the tag as the version number. Since a git tag points to a specific state of the code, I can easily check out the code corresponding to a version, to locate a bug, for instance. I can also browse all the changes between two versions.
If you have any kind of non-trivial project, you will want to at least run a CI. And even a basic CD will probably help you in tracking changes from a released piece of software back to the corresponding code in your code history.