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AE is an assertions framework. It was designed to serve as a reusable domain language for other test frameworks, such as QED and Cucumber. Essentially AE defines the method assert. The method is compatible with the same method as defined by Test::Unit and minitest which verifies truth of a single argument (and can accept an optional failure message).

  assert( true )

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

  assert{ true }

But the real power the AE’s assert method lies in it’s use without an argument or a block. In that case it returns an instance of Assertor. An Assertor is an Assertions Functor, or Higher-Order Function —a function that operates on another function. With it, we easily make assertions with a fluent notation.

  x.assert == y

  a.assert.include? e

  StandardError.assert.raised? do
    ...
  end

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

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

  "Daffy Duck".assert.daffy?

In addition to assert, AE provides the assertion method, expect. It works much like assert but uses #=== to evaluate success. This allows for some useful flexibility in making assertions. For instance, it can be used to test for a matching regular expression.

    expect /t/ do
      "tom"
    end

Even more useful, #expect will catch exceptions when a exception class is provided.

    expect ArgumentError do
      raise ArgumentError
    end

In this example the ArgumentError will be caught, and the assertion successful. While essentially the same as using ArgumentError.assert.raised?, expect is a bit more concise.

Additional Support Libraries

AE also provides some optional support libraries, including subjunctive forms, such as #should, and legacy assertions for backward compatibility with Test::Unit’s assertion methods.

Further Reading

Please have a look at the QED generated Demonstrandum or the RDoc generated API Documentation to learn more.

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