module Minitest::Assertions

def self.diff
  return @diff if defined? @diff
  @diff = if (RbConfig::CONFIG["host_os"] =~ /mswin|mingw/ &&
              system("diff.exe", __FILE__, __FILE__)) then
            "diff.exe -u"
          elsif system("gdiff", __FILE__, __FILE__)
            "gdiff -u" # solaris and kin suck
          elsif system("diff", __FILE__, __FILE__)
            "diff -u"
          else
            nil
          end
end