Test to reproduce the problems we were having with FakeFS in the minitest-rails tests. Use version 0.5.0 of FakeFS, and whatever the current version of Thor is.

test_fakefs_thor.rb

require "minitest/autorun"
require "thor"
require "fakefs/safe"

class SampleGenerator < Thor::Group
  include Thor::Actions
  def start *args
    template "foo.erb", "new/path/here/foo.rb"
  end
end

class TestFakeFSThor < Minitest::Test
  def setup
    @dir = Dir.pwd
    `touch foo.erb`
  end

  def test_thor
    SampleGenerator.source_root @dir
    out, err = capture_io do
      SampleGenerator.new.start "thor"
    end
    assert_match /new\/path\/here\/foo.rb/, out
  end

  def test_thor_with_fakefs
    FakeFS.activate!
    # Uncommenting the following will make it pass
    #FakeFS::FileSystem.dir_levels.delete "/"
    FakeFS::FileSystem.clone @dir

    test_thor
  ensure
    FakeFS::FileSystem.clear
    FakeFS.deactivate!
  end
end

Hat tip to @zenspider for isolating the issue to "/" being in the dir_levels array.