Expect

gem install expectations

A short presentation is hosted at Github.

Documentation is available at rubydoc.info.

This function expects a String argument starting with "http:", an Integer or Float argument, and a Hash with a String entry at key :foo, and either an Array or nil at key :bar.

def function(a, b, options = {})
  expect! a => /^http:/, 
          b => [Integer, Float], 
          options => {
            :foo => String,
            :bar => [ Array, nil ]
          }
end

The expectations gem is distributed under the terms of the Modified BSD License, see LICENSE.BSD for details.