def util_setup_spec_fetcher(*specs)
    specs -= Gem::Specification._all
    Gem::Specification.add_specs(*specs)

    spec_fetcher = Gem::SpecFetcher.fetcher

    prerelease, _ = Gem::Specification.partition { |spec|
      spec.version.prerelease?
    }

    spec_fetcher.specs[@uri] = []
    Gem::Specification.each do |spec|
      spec_tuple = [spec.name, spec.version, spec.original_platform]
      spec_fetcher.specs[@uri] << spec_tuple
    end

    spec_fetcher.latest_specs[@uri] = []
    Gem::Specification.latest_specs.each do |spec|
      spec_tuple = [spec.name, spec.version, spec.original_platform]
      spec_fetcher.latest_specs[@uri] << spec_tuple
    end

    spec_fetcher.prerelease_specs[@uri] = []
    prerelease.each do |spec|
      spec_tuple = [spec.name, spec.version, spec.original_platform]
      spec_fetcher.prerelease_specs[@uri] << spec_tuple
    end

    v = Gem.marshal_version

    Gem::Specification.each do |spec|
      path = "#{@gem_repo}quick/Marshal.#{v}/#{spec.original_name}.gemspec.rz"
      data = Marshal.dump spec
      data_deflate = Zlib::Deflate.deflate data
      @fetcher.data[path] = data_deflate
    end unless Gem::RemoteFetcher === @fetcher # HACK for test_download_to_cache

    nil # force errors
  end
#
Sets up Gem::SpecFetcher to return information from the gems in +specs+.
Best used with +@all_gems+ from #util_setup_fake_fetcher.