Repeating RSpec example groups with different arguments

metaprogramming, rspec, ruby

Solution

So (apologies if I'm repeating stuff you already know) but every time you call describe/context rspec creates a new class that is a subclass of the current example group class (which eventually is a subclass of `RSpec::Core::ExampleGroup`) and then uses `module_eval` to evaluate the block in the context of that class. If I run

describe "foo" do
  puts "#{self}; #{self.superclass}"
  describe "behaviour 1" do
    puts "#{self}; #{self.superclass}"
    context "with x" do
      puts "#{self}; #{self.superclass}"
    end
  end
end

then the output is

#<Class:0x007fb772bfbc70>; RSpec::Core::ExampleGroup
#<Class:0x007fb772bfb180>; #<Class:0x007fb772bfbc70>
#<Class:0x007fb772bfa5f0>; #<Class:0x007fb772bfb180>

When you call `it` rspec create an `Example` object and appends it to a class instance variable on self (the current example group). rspec also sticks the current example group in the example's metadata, walking up this tree of example groups is what gives you the full description of the example.

Your `repetitively_describe` method calls `describe`, so at the point that you call `example_group_block.call item` self is indeed the freshly created example group. When the proc gets evaluated, it of course remembers what the value of `self` was when it was called so your calls to `it` are made to the example group that was current when repetitively_describe (easily verifiable by sprinkling some calls to check the value of self throughout your code). Similarly a call to describe adds the example group as a child of the outer example group, not the one created by `repetitively_describe`.

What you of course need to do is call `example_group_block` preserving the correct value of self.

module RepetitivelyDescribe
  def repetitively_describe(*args, &example_group_block)
    options = args.extract_options!
    options.delete(:for).each do |item|
      item_args = args.collect(&:dup) + [options.dup]
      item_args[0] << " [#{item}]"

      describe(*item_args) do
        class_exec(item, &example_group_block)
      end
    end
  end
end

with this change

describe('foo') do
  repetitively_describe "Query API", :for => %w( v1 v2 ) do |version|
    it "responds with JSON"
  end
end.descendant_filtered_examples.collect(&:full_description)

outputs `["foo Query API [v1] responds with JSON", "foo Query API [v2] responds with JSON"]` instead of `["foo responds with JSON", "foo responds with JSON"]` before the change.

Problem

Original source