How to include unit tests in a ruby module?

Question

I'm trying to include the unit tests for a module in the same source file as the module itself, following the Perl modulino model.

#! /usr/bin/env ruby

require 'test/unit'

module Modulino
    def modulino_function
        return 0
    end
end

class ModulinoTest < Test::Unit::TestCase
    include Modulino
    def test_modulino_function
        assert_equal(0, modulino_function)
    end
end

Now, I can run the unit-tests executing this source file.

But, they are also run when I require/load them from another script. How can this be avoided ?

Is there a more idiomatic way to achieve this with Ruby, unless this practice is discouraged ?

Answer 1

Personally I've never heard of anyone trying to do this in Ruby. It's definitely not a standard practice. That said you may be able to leverage this trick:

if __FILE__ == $0
  # Do something.. run tests, call a method, etc. We're direct.
end

The code in the if block will only execute if the file is executed directly, not if it's required by another library or application.

More ruby tricks here: http://www.rubyinside.com/21-ruby-tricks-902.html

Answer 2

You can include unit tests inside the module source code itself using minitest.

Try this example:

class Foo < String
end

if $0 == __FILE__
    require 'minitest/autorun'
    require 'minitest/pride'

    class FooTest < MiniTest::Unit::TestCase
        def test_foo_instantiation
            foo = Foo.new()
            assert_instance_of Foo, foo
        end

        def test_foo_parent_class
            foo = Foo.new()
            assert_kind_of String, foo
        end
    end
end

Here I created a class called Foo, which inherits from the class String. Then I created two unit tests. In the first test, I check that I can instantiate an object of class Foo. In the second test, I check that the instantiated object of class Foo is a kind of String.

If this code is written in a file called foo.rb, I can simply run the tests using this command:

ruby foo.rb

Minitest is fast to execute. The "pride" module allows you to output the test result in color fonts, which is nice on the eye.

Answer 3

It's actually not that uncommon in Ruby though it's certainly not the common practice in Rails.

One of the issues you may be running into is the same as this post which is that modules really should be included in classes in order to test them. It's certainly possible to test a module by including it in your test case but you're testing whether the module works when mixed into Test::Unit::TestCase, not that it'll work when you mix it into something more useful.

So unit tests should probably live on the class file or if you just want generally available methods use a class function instead of a module.

Answer 4

Just found one way to prevent the unit test from being executed when the module is required from a script. There is a flag in unit.rb in .../lib/ruby/1.8/test/ to set to true.

Combined with samg trick (thanks again), we can write:

if (__FILE__ != $0)
    Test::Unit.run = true  ### do not run the unit tests
end