Fixes #42 - Rails 4.2 beta has deprecated capture

Thanks @cupakromer for this fix re-implementing `capture` now that Rails 4.2 has made it private.

lib/ammeter/init.rb

@@ -3,6 +3,7 @@
   require 'ammeter/rspec/rspec_2_compatibility'  # if rspec2
 end
 require 'rails'
+require 'ammeter/output_capturer.rb'
 require 'ammeter/rspec/generator/example.rb'
 require 'ammeter/rspec/generator/matchers.rb'
 

lib/ammeter/output_capturer.rb

@@ -0,0 +1,40 @@
+module Ammeter
+  class OutputCapturer
+    # Is this thread safe!?!?
+    # This won't work with sub-processes
+    def self.capture(io, &block)
+      case io
+      when :stdout
+        capture_stdout(&block)
+      when :stderr
+        capture_stderr(&block)
+      else
+        raise "Unknown IO #{io}"
+      end
+    end
+
+    def self.capture_stdout(&block)
+      captured_stream = StringIO.new
+
+      orginal_io, $stdout = $stdout, captured_stream
+
+      block.call
+
+      captured_stream.string
+    ensure
+      $stdout = orginal_io
+    end
+
+    def self.capture_stderr(&block)
+      captured_stream = StringIO.new
+
+      orginal_io, $stderr = $stderr, captured_stream
+
+      block.call
+
+      captured_stream.string
+    ensure
+      $stderr = orginal_io
+    end
+  end
+end

lib/ammeter/rspec/generator/example/generator_example_group.rb

@@ -13,7 +13,7 @@ module GeneratorExampleGroup
         extend ActiveSupport::Concern
         include ::RSpec::Rails::RailsExampleGroup
 
-        DELEGATED_METHODS = [:capture, :destination_root, :current_path, :generator_class]
+        DELEGATED_METHODS = [:destination_root, :current_path, :generator_class]
         module ClassMethods
           mattr_accessor :test_unit_test_case_delegate
           delegate :default_arguments, :to => :'self.test_unit_test_case_delegate'
@@ -44,12 +44,12 @@ def generator(given_args=self.default_arguments, config={})
           end
 
           def run_generator(given_args=self.default_arguments, config={})
-            capture(:stdout) { generator(given_args, config).invoke_all }
+            OutputCapturer.capture(:stdout) { generator(given_args, config).invoke_all }
           end
         end
 
         def invoke_task name
-          capture(:stdout) { generator.invoke_task(generator_class.all_tasks[name.to_s]) }
+          OutputCapturer.capture(:stdout) { generator.invoke_task(generator_class.all_tasks[name.to_s]) }
         end
 
         included do