There are a number of situations where matchers are invaluble, such as UI validation, or data filtering, but it is in the area of writing flexible tests that matchers are most commonly used.

His example that checks to see if one object is equal to another object. The Hamcrest matcher allows for a "assertThat" method making it easier to create and use pre-existing unit testing assertions.

He also includes a list of some of the most common matchers broken up into groups of core, logical, object, number and text.

I have begun to port Hamcrest, which provides a library of matcher objects (also known as constraints or predicates) allowing "match" rules to be defined declaratively, to be used in other frameworks. Typical scenarios include testing frameworks, mocking libraries and UI validation rules, to PHP.

The hamcrest-php project compliments other current hamcrest-related projects and his ultimate goal is to make it available to the PHPUnit testing community (as well as with the PHPMock effort).