 JUnit is linked as a JAR at compile-time; the framework resides under package codice_1 for JUnit 3.8 and earlier, and under package codice_2 for JUnit 4 and later.A research survey performed in 2013 across 10,000 Java projects hosted on GitHub found that JUnit (in a tie with slf4j-api), was the most commonly included external library.Each library was used by 30.7% of projects.