We are obviously in the age of Microservices, Mobile first, Polyglot, post-Java JVM languages, GitHub and Docker uprise. In this world, Open Source usage dominates, and the speed of change is intense. Knowing the direction of DevOps tools and picking the right one for the project is crucial.
Continuous Integration is the practice of running your tests on a non-developer machine automatically everytime someone pushes new code into the source repository.
This has the tremendous advantage of always knowing if all tests work and getting fast feedback. The fast feedback is important so you always know right after you broke the build (introduced changes that made either the compile/build cycle or the tests fail) what you did that failed and how to revert it.