FakeFS

# File lib/fakefs/base.rb, line 7
def self.activate!
  Object.class_eval do
    remove_const(:Dir)
    remove_const(:File)
    remove_const(:FileTest)
    remove_const(:FileUtils)

    const_set(:Dir,       FakeFS::Dir)
    const_set(:File,      FakeFS::File)
    const_set(:FileUtils, FakeFS::FileUtils)
    const_set(:FileTest,  FakeFS::FileTest)
  end
  true
end

# File lib/fakefs/base.rb, line 22
def self.deactivate!
  Object.class_eval do
    remove_const(:Dir)
    remove_const(:File)
    remove_const(:FileTest)
    remove_const(:FileUtils)

    const_set(:Dir,       RealDir)
    const_set(:File,      RealFile)
    const_set(:FileTest,  RealFileTest)
    const_set(:FileUtils, RealFileUtils)
  end
  true
end