Syntax Sugar for Defining Test Helper Methods

I prefer Ruby's Test::Unit over RSpec, but one of the things I like about RSpec is the let method. It allows you to create memoized helper methods in your tests.

Here's a way to do that in Test::Unit:

class Test::Unit::TestCase
  def self.let(name, &block)
    ivar = "@#{name}"
    self.class_eval do
      define_method(name) do
        if instance_variable_defined?(ivar)
          instance_variable_get(ivar)
        else
          value = self.instance_eval(&block)
          instance_variable_set(ivar, value)
        end
      end
    end
  end
end

Now instead of writing helper methods in your tests like this...

class EmployeeTest < Test::Unit::TestCase
  def test_employee_has_an_email
    assert_equal('jdoe@example.com', employee.email)
  end

  private

  def employee
    @employee ||= Employee.new('jdoe@example.com')
  end  
end

You can use "let" like this...

class EmployeeTest < Test::Unit::TestCase
  let(:employee) { Employee.new('jdoe@example.com') }

  def test_employee_has_an_email
    assert_equal('jdoe@example.com', employee.email)
  end
end