Guava is a suite of core and expanded libraries that include

A library to query and verify JSON

Apache Commons Net library contains a collection of network utilities and protocol implementations.

Java DSL for easy testing of REST services

Alternate implementations of JDK's "Math" functions.

Apache HttpComponents Client fluent API

The Apache Mailet API is a flexible specification for mail processing agents.

Apache James Mailet Test is a collection of utilities to help testing mailets.

Root project for all james modules that run tests

A Java DSL for synchronizing asynchronous operations

Core package for the JUnit Jupiter test engine.

Isolated container management for Java code testing

SubEtha SMTP is an easy-to-use server-side SMTP library for Java.