Custom RSpec Contexts

Sometimes it can be useful to have custom RSpec contexts. In a recent project, a library which matches Strings to pick up dates mentioned in the string, I really wanted to write tests like:

thoughts_on Date.today do
  think 'Tomorrow at noon', Date.tomorrow
  think 'Today is the best', Date.today
  # ... a bunch more of the same
end

.. no writing the same if’s over and over again

Furthermore, I wanted to do it in a reusable way, so that I wouldn’t need to be defining methods inside of these blocks. I wanted the tests to just get across the data that was needed (in this case, the date in question, and the before & after state for a transformation)

What I ended up learning, is that in RSpec, context and describe return their evaluation objects. So, I were a Module and a def from what I wanted:

module ThoughtMethods
  attr_accessor :pickup_parser
  def think(phrase, reference)
    parser = pickup_parser
    it "should see #{phrase} as #{reference}" do
      parser.locate(phrase).should == reference
    end
  end
end

def thoughts_on(today, &block)
  example_class = describe "on #{today}"
  example_class.extend ThoughtMethods
  example_class.pickup_parser = Pickup::Parser.new(today)
  example_class.class_eval &block
end

It’s nice because you still get all of the same output & separation, with none of the awkward fluff.