Assertive Expressive

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Assertive Expressive (AE) is an assertions framework intended for reuse by any TDD, BDD or similar system.


  • Clear, simple and concise syntax.

  • Uses higher-order functions and fluid notation.

  • Reusable core extensions ease assertion construction.

  • Core extensions are standardized around Ruby Facets.

  • But Facets is not a dependency; the extensions are built-in.

  • Easily extensible allowing for alternate notations.

  • Eats it's own dog food.


AE defines the method assert. It's is compatible with the method as defined by Test::Unit and MiniTest, which verifies truth of a single argument (and can accept an optional failure message).


In addition AE's assert method has been extended to accept a block, the result of which is likewise verified.


But the real power the AE's assert method lies in it's use without argument or block. In that case it returns an instance of Assertor. An Assertor is an Assertions Functor, or Higher-Order Function. It is a function that operates on another function. With it, we can make assertions like so:

x.assert == y

a.assert.include? e

StandardError.assert.raised? do

And so forth. Any method can be used in conjunction with assert to make an assertion. Eg.

class String
  def daffy?
    /daffy/i =~ self

"Daffy Duck".assert.daffy?

When an assertion fails an Assertion exception is raised. Any test framework can catch this exception and process it accordingly. Technically the framework should check to see that the exception object responds affirmatively to the #assertion? method. This way any type of exception can be used as a means of assertion, not just AE's Assertion class.

Please have a look at the QED and API documentation to learn more.


Generally speaking, AE can be used with any test framework simply by putting require 'ae' in a test helper script. However to fully integrate with a test framework and ensure the test framework recognizes AE assertions (as more than just exceptions) and to ensure assertion counts are correct, a little extra interfacing code may be necessary.

Lucky for you AE has already done the leg work for the most common test frameworks:

require 'ae/adapters/testunit'
require 'ae/adapters/minitest'
require 'ae/adapters/rspec'

(Note that Cucumber does not need an adapter.)

AE also includes a script that will automatically detect the current test framework by checking for the existence of their respective namespace modules.

require 'ae/adapter'


With AE, defining assertions centers around the #assert method. So assert can be thought of as AE's primary nomenclature. However, variant nomenclatures have been popularized by other test frameworks, in particular should and must. If you prefer one of them terms, AE provides optional libraries that can loaded for utilizing them.

require 'ae/should'
require 'ae/must'

By loading one of these scripts (or both) into your test system (e.g. via a test helper script) you gain access to subjunctive terminology. See the API documentation for the Subjunctive module for details.


To ease transition from TestUnit style assertion methods, AE provides a TestUnit legacy module.

require 'ae/legacy'

This provides a module `AE::Legacy::Assertions` which is included in AE::World and can be mixed into your test environment to provide old-school assertion methods, e.g.

assert_equal(foo, bar, "it failed")


Gem Installs

Install AE in the usual fashion:

$ gem install ae

Site Installs

Local installation requires Setup.rb.

$ gem install setup

Then download the tarball package from GitHub and do:

$ tar -xvzf ae-1.0.0.tgz
$ cd ae-1.0.0.tgz
$ sudo setup.rb all

Windows users use 'ruby setup.rb all'.


(BSD-2-Clause License)

Copyright © 2008,2010 Thomas Sawyer

Unless otherwise provided for by the originating author, this program is distributed under the terms of the BSD-2-Clause license. Portions of this program may be copyrighted by others.

See the NOTICE.rdoc file for details.

AE is a Rubyworks project.