A draft implementation for descriptive predicates based on JDK8.

Inspired by hamcrest.

Descriptive predicates consists of three important aspects;

• it acts as a Predicate<T> for a type T,
• it provides a descriptive message for that predicate, i.e. it has a descriptive toString(), and
• it acts as a describer for a type T, i.e Function<T, String>

Descriptive predicates can be used wherever a regular Java 8 Predicate<T> can be used, but are particularly useful in some scenarios.

Testing, i.e:

verifyThat(result, greaterThan(4));

Input validation (i.e in production code):

validate(input, greaterThan(4), otherwiseThrowing(BadRequest.class));

Design by contract (i.e assertions in production code):

require(input, greaterThan(4));
...
ensure(output, greaterThan(5));