Continuous Integration was first introduced in the year 2000 with the software known as Cruise Control. Over the years, Continuous Integration has become a key practice in any software organization. This is a development practice that calls upon development teams to ensure that a build and subsequent testing is conducted for every code change made to a software program. This concept was meant to remove the problem of finding late occurrences of issues in the build lifecycle. Instead of the developers working in isolation and not integrating enough, Continuous Integration was introduced to ensure that the code changes and builds were never done in isolation.

Why Continuous Integration?

Continuous integration has become a very integral part of any software development process. The continuous Integration process helps to answer the following questions for the software development team.

Do all the software components work together as they should? Sometimes systems can become so complex that there are multiple interfaces for each component. In such cases, its always critical to ensure that all the software components work seamlessly with each other.
Is the code too complex for integration purposes? If the continuous integration process keeps on failing, there could be a possibility that the code is just too complex. And this could be a signal to apply proper design patterns to make the code lesser complex and more maintainable.
Does the code adhere to the established coding standards? Most of the test cases will always check that the code is adhering to the proper coding standards. By doing an automated test after the automated build, this is a good point to check if the code meets all the desired coding standards.
How much code is covered by automated tests? There is no point in testing code if the test cases dont cover the required functionality of the code. So its always a good practice to ensure that the test cases written should cover all the key scenarios of the application.
Were all the tests successful after the latest change? If a test fails, then there is no point in proceeding with the deployment of the code, so this is a good point to check if the code is ready to move to the deployment stage or not.

Workflow

The following image shows a quick workflow of how the entire Continuous Integration workflow works in any software development project. We will look at this in detail in the subsequent chapters.

So, based on the above workflow, this is generally how the continuous integration process works.

First, a developer commits the code to the version control repository. Meanwhile, the Continuous Integration server on the integration build machine polls source code repository for changes (e.g., every few minutes).
Soon after a commit occurs, the Continuous Integration server detects that changes have occurred in the version control repository, so the Continuous Integration server retrieves the latest copy of the code from the repository and then executes a build script, which integrates the software
The Continuous Integration server generates feedback by e-mailing build results to the specified project members.
Unit tests are then carried out if the build of that project passes. If the tests are successful, the code is ready to be deployed to either the staging or production server.
The Continuous Integration server continues to poll for changes in the version control repository and the whole process repeats.

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