Continuous integration (CI) is a software engineering practice in which isolated changes are immediately tested and reported on when they are added to a larger code base. The goal of CI is to provide rapid feedback so that if a defect is introduced into the code base, it can be identified and corrected as soon as possible. Continuous integration software tools can be used to automate the testing and build a document trail.
Continuous integration has evolved since its conception. Originally, a daily build was the standard. Now, the usual rule is for each team member to submit work on a daily (or more frequent) basis and for a build to be conducted with each significant change. When used properly, continuous integration provides various benefits, such as constant feedback on the status of the software. Because CI detects deficiencies early on in development, defects are typically smaller, less complex and easier to resolve.
According to Paul Duvall, co-author of Continuous Integration: Improving Software Quality and Reducing Risk, best practices of CI include:
Committing code frequently.
Categorizing developer tests.
Using a dedicated integration build machine.
Using continuous feedback mechanisms.
CI originated from within the extreme programming paradigm but the principles can be applied to any iterative programming model, such as agile programming. Traditional development approaches, such as the waterfall model can benefit from using CI methods for the construction stage.