Hamcrest is a library of matchers, which can be combined in to create flexible expressions of intent in tests.

See:
Description

Hamcrest API and Utility Classes

org.hamcrest

The stable API defining Matcher and its associated interfaces and classes.

Matcher Library

org.hamcrest.beans	Matchers of Java Bean properties and their values.
org.hamcrest.collection	Matchers of arrays and collections.
org.hamcrest.core	Fundamental matchers of objects and values, and composite matchers.
org.hamcrest.internal
org.hamcrest.number	Matchers that perform numeric comparisons.
org.hamcrest.object	Matchers that inspect objects and classes.
org.hamcrest.text	Matchers that perform text comparisons.
org.hamcrest.xml	Matchers of XML documents.

Integration

org.hamcrest.integration

Hamcrest is a library of matchers, which can be combined in to create flexible expressions of intent in tests.

Documentation can be found at: http://hamcrest.org/.