test.rb

require "test/unit"

Module.send :include, Module.new {
  def test(name, &block)
    define_method("test_#{name.gsub(/[^a-z0-9]/i, "_")}".to_sym, &block)
  end
  alias :should :test
}

module NumericTests
  test "should do addition" do
    assert_equal 2, @this + 1
  end
end

class IntegerTest < Test::Unit::TestCase
  include NumericTests

  def setup
    @this = 1
  end
end

class FloatTest < Test::Unit::TestCase
  include NumericTests

  def setup
    @this = 1.0
  end
end