all_be.rb

# Allow RSpec assertions over the elements of a collection.  For example:
#
#   collection.should all_be > 0
#
# will specify that each element of the collection should be greater
# than zero.  Each element of the collection that fails the test will
# be reported in the error message.
#
# Examples:
#   [1,1,1].should all_be eq(1)
#   [2,4,6].should all_be_even
#   [3,6,9].should all_be_divisible_by(3)
#   [1,1,1].should all_be == 1
#   [2,3,5].should all_be { |n| prime?(n) }
#
# (for appropriate definitions of prime? and divisible_by?)
#
module RSpec
  module Matchers

    # Helper functions gathered here to avoid global name space
    # pollution.
    module AllBe
      module_function

      # Format a predicate function (with option arguments) for human
      # readability.
      def format_predicate(pred, *args)
        message_elements =
          ["be #{pred.gsub(/_/, ' ')}"] +
          args.map { |a| a.inspect }
        message_elements.join(' ')
      end

      # Create a collection matcher using +block+ as the matching
      # condition.  Block should take one or two arguments:
      #
      #   lambda { |element| ... }
      #   lambda { |element, messages| ... }
      #
      # If a block wishes to use custom failure messages, it should
      # append the message to the +messages+ array.  Otherwise we will
      # format an appropriate error message for each failing element.
      #
      def make_matcher(condition_string, &block)
        Matcher.new :all_be, block do |_block_|
          @failing_messages = []
          @broken = []
          match do |actual|
            actual.each do |element|
              unless _block_.call(element, @failing_messages)
                @broken << element
              end
            end
            @broken.empty?
          end

          failure_message_for_should do |actual|
            messages = ["in #{actual.inspect}:"]
            if @failing_messages.empty?
              messages += @broken.map { |element| "expected #{element.inspect} to #{condition_string}" }
            else
              messages += @failing_messages
            end
            messages.join("\n")
          end

          failure_message_for_should_not do |actual|
            "expected #{actual.inspect} to not all #{condition_string}"
          end

          description do
            "all be"
          end
        end
      end
    end

    # Handle mapping operators to appropriate collection mappers.
    class AllBeOperatorMatcher
      [:==, :!=, :>, :<, :<=, :>=].each do |op|
        define_method(op) do |value|
          AllBe.make_matcher("be #{op} #{value}") { |element|
            element.send(op, value)
          }
        end
      end
    end

    alias method_missing_without_all_be method_missing

    # Handle all_be_XXX predicates.  If it doesn't match the
    # all_be_XXX pattern, delegate to the existing method missing
    # handler.
    def method_missing(sym, *args, &block)
      if sym.to_s =~ /^all_be_(\w+)$/
        pred = $1
        pred_method = "#{pred}?"
        pred_string = AllBe.format_predicate(pred, *args)
        AllBe.make_matcher(pred_string) { |element|
          element.send(pred_method, *args, &block)
        }
      else
        method_missing_without_all_be(sym, *args, &block)
      end
    end

    # Return a matcher appropriate for matching across elements of a
    # collection.
    def all_be(matcher=nil, &block)
      if matcher
        AllBe.make_matcher("pass") { |element, messages|
          if matcher.matches?(element)
            true
          else
            messages << matcher.failure_message_for_should
            false
          end
        }
      elsif block_given?
        AllBe.make_matcher("satisfy the block", &block)
      else
        AllBeOperatorMatcher.new
      end
    end
  end
end

Hiya Jim... Maybe I'm just being anal, but shouldn't "method_missing_without_be_all" be "method_missing_without_all_be"? It seems that you're using _all_be everywhere else...

Line 116 too...

"Foolish consistency is the hobgoblin of little minds" -- Emerson

But you're right. Thanks.

Consistency != Foolishness. The reason for the consistency I suggested is that it makes your code more comprehensible. Like written prose, consistent and well-written code is reflective of consistent and well-reasoned thinking.

I don't think putting someone who is trying to help improve your code in a defensive position is behavior that will encourage future commenting or a future desire to help.

Ok, the version here is cleaned up and now handing the edgecases.

OFdtripp: My apologies. I meant that as a playful commentary (after all, I did admit you were correct). I apologize for not successfully communicating that your comment was indeed welcome.

There is only one question i got when reading this: why to create it at all? Any reason for not using "all?" with RSpec? Did you just want to try it out how complex or easy would it be to create such a matcher or what was the initial purpose?

I would have saved 127 lines of code and used vanilla RSpec like this:
[1,1,1].should be_all {|e| e == 1}
[2,4,6].should be_all {|e| e % 3 == 0}

I guess you know how this continues.

Several reasons:

1. To explore RSpec matchers in depth
2. To demonstrate how much work this faux-english approach actually takes (as you point out, 127 lines of rather dense code)
3. To get better error messages (see example below)

Better error messages:
Given:

describe Array do
  subject { [2,3,4,5] }
  it { should be_all { |n| n.even? } }
  it { should all_be_even }
end

The be_all version reports:

  1) Array 
     Failure/Error: it { should be_all { |n| n.even? } }
     expected all? to return true, got false
     # ./xx_spec.rb:5:in `block (2 levels) in <top (required)>'

The all_be version reports:

  2) Array 
     Failure/Error: it { should all_be_even }
     in [2, 3, 4, 5]:
     expected 3 to be even
     expected 5 to be even
     # ./xx_spec.rb:6:in `block (2 levels) in <top (required)>'