Cuando una assertion falla

[~/local/src/ruby/LPP/unit_testing/simple_example(master)]$ cat test/tc_simple_number2.rb 
# File:  tc_simple_number2.rb
 
require "simple_number"
require "test/unit"
 
class TestSimpleNumber < Test::Unit::TestCase
 
  def test_simple
    assert_equal(4, SimpleNumber.new(2).add(2) )
    assert_equal(4, SimpleNumber.new(2).multiply(2) )
  end
 
  def test_typecheck
    assert_raise( RuntimeError ) { SimpleNumber.new('a') }
  end
 
  def test_failure
    assert_equal(3, SimpleNumber.new(2).add(2), "Adding doesn't work" )
  end
 
end

[~/local/src/ruby/LPP/unit_testing/simple_example(master)]$ cat Rakefile 
desc "Test class SimpleNumber"
task :test do
  sh "ruby -Ilib -Itest test/tc_simple_number.rb"
end

desc "Test with test/tc_simple_number2.rb. Expect failures"
task :test2 do
  sh "ruby -Ilib -Itest test/tc_simple_number2.rb"
end

[~/local/src/ruby/LPP/unit_testing/simple_example(master)]$ rake test2
ruby -Ilib -Itest test/tc_simple_number2.rb
Run options: 

# Running tests:

F..

Finished tests in 0.001706s, 1758.4994 tests/s, 2344.6659 assertions/s.

  1) Failure:
test_failure(TestSimpleNumber) [test/tc_simple_number2.rb:18]:
Adding doesn't work.
<3> expected but was
<4>.

3 tests, 4 assertions, 1 failures, 0 errors, 0 skips
rake aborted!
Command failed with status (1): [ruby -Ilib -Itest test/tc_simple_number2.r...]
/Users/casiano/local/src/ruby/LPP/unit_testing/simple_example/Rakefile:8:in `block in <top (required)>'
/Users/casiano/.rvm/gems/ruby-1.9.3-p392/bin/ruby_noexec_wrapper:14:in `eval'
/Users/casiano/.rvm/gems/ruby-1.9.3-p392/bin/ruby_noexec_wrapper:14:in `<main>'
Tasks: TOP => test2
(See full trace by running task with --trace)

1. Now there are three tests (three member functions) in the class.

2. The function test_typecheck uses assert_raise to check for an exception.

3. The function test_failure is set up to fail, which the Ruby output happily points out, not only telling us which test failed, but how it failed (expected <3> but was <4>).

4. On this assertion, we've also added an final parameters which is a custom error message. It's strictly optional but can be helpful for debugging.

5. All of the assertions include their own error messages which are usually sufficient for simple debugging.