Coveralls is an application that allows developers to get an overview of the extend of their projects' automated test coverage.
The application works with your continuous integration service / server to provide constant updates on your project's automated test coverage, and provide fine-grained code-coverage statistics on all of your repositories include the total percentages covered, the lines covered, test coverage on a file by file basis, covered and missed lines, and the hits per line for each file in your source code repository. Using the Coveralls badge for your GitHub readme allows the development community to see just how covered your code is.
Automated testing has become such an important part of software development, and Coveralls lets you show off the hard work you put into your testing suite. Because a coverage lapse can sink apps.