[Updated to Sept 5, 2009]

Did you know that rspec is interoperable with test/unit?

spec/rails (formerly rspec_on_rails) has always run on test/unit and rspec (core) has had t/u interop capability for over a year now.

Take, for example, this test in addition_test.rb:

require 'test/unit'

class TestAddition < Test::Unit::TestCase
def test_add_1_and_2
  assert_equal 3, 1 + 2
end
end







$ ruby addition_test







Loaded suite /Users/david/projects/ruby/tmp/tur/addition_test
Started
.
Finished in 0.000289 seconds.

1 tests, 1 assertions, 0 failures, 0 errors

Now, simply require ‘spec/test/unit’:

require 'rubygems'
require 'spec/test/unit'

class TestAddition < Test::Unit::TestCase
def test_add_1_and_2
  assert_equal 3, 1 + 2
end
end

Run it with the spec command that is installed when you install rspec:

$ spec addition_test

And tada!

.

Finished in 0.001451 seconds

1 example, 0 failures

RSpec is running your tests!

So why would you do this? Well, for starters, now you can run this with any of RSpec’s command line options. This prints out the name of each test class and test method:

$ spec addition_test.rb --format specdoc

TestAddition
- test_add_1_and_2

1 example, 0 failures

Try it with html:

$ spec addition_test_with_rspec.rb --format html:report.html

Now open up report.html and voila!

Wanna should in your tests?

def test_add_1_and_2
(1 + 2).should == 3
end

Wanna assert in your rspec code examples?

describe "adding in Ruby" do
it "returns 3 for 2 + 1" do
  assert_equal 3, 1 + 2
end
end

When you invoke rspec’s test/unit bridge, rspec and test/unit become completely interoperable. This means that most of the extensions and plugins for both libraries are available to you at the same time. I say most because libs that monkey patch their way into internals of either don’t always play nice in this environment.

This also means that transitioning from an existing test/unit suite to an rspec suite is as simple as changing a single require statement and then gradually changing the tests to rspec code examples. You can run them all together during this refactoring, so you don’t have to do this all at once, and you can keep moving on your project with little to no penalty.

So if you’re choosing an alternative framework because you prefer its syntax, more power to you. If you’re choosing it because you understand its internals better, right on! Have at it. But if you’re choosing it only because it plays nice with test/unit and you didn’t know that rspec does as well, well, now you know.