initializer.rb

def in_memory_database?
  ENV["RAILS_ENV"] == "test" and 
    ENV["IN_MEMORY_DB"] and
    Rails::Configuration.new.database_configuration['test-in-memory']['database'] == ':memory:'
end

$TESTING=true

if in_memory_database?
  puts "connecting to in-memory database ..."
  ActiveRecord::Base.establish_connection(Rails::Configuration.new.database_configuration['test-in-memory'])
  puts "building in-memory database from db/schema.rb ..."
  load "#{Rails.root}/db/schema.rb" # use db agnostic schema by default
  #  ActiveRecord::Migrator.up('db/migrate') # use migrations
end

spec_suite_in_parallel.rb

require "spec/spec_helper"

GEO_SPECS = Dir["spec/geocoding/**/*_spec.rb"]
SOLR_SPECS = Dir["spec/solr/**/*_spec.rb"]

EXCLUDED_SPECS = GEO_SPECS + SOLR_SPECS

if ENV['IN_MEMORY_DB']
  N_PROCESSES = 2 # for dual-core machines
  specs = (Dir["spec/**/*_spec.rb"] - EXCLUDED_SPECS).sort.in_groups_of(N_PROCESSES)
  processes = []

  interrupt_handler = lambda do
    STDERR.puts "caught keyboard interrupt, exiting gracefully ..."
    processes.each { |process| Process.kill "KILL", process }
    exit 1
  end

  Signal.trap 'SIGINT', interrupt_handler
  1.upto(N_PROCESSES) do |j|
    processes << Process.fork {
      specs.each do |array|
        if array[j-1]
          require array[j-1]
        end
      end
    }
  end
  1.upto(N_PROCESSES) { Process.wait }

else
  (Dir["spec/**/*_spec.rb"] - EXCLUDED_SPECS).each do |file|
    require file
  end
end