JUnit is a unit testing framework for Java, created by Erich Gamma and Kent Beck.
Standard library for the Scala Programming Language
Guava is a suite of core and expanded libraries that include utility classes, google's collections, io classes, and much much more. Guava has only one code dependency - javax.annotation, per the JSR-305 spec.
The Apache Commons IO library contains utility classes, stream implementations, file filters, file comparators, endian transformation classes, and much more.