FakeFS

Mocha is great. But when your library is all about manipulating the filesystem, you really want to test the behavior and not the implementation.

If you're mocking and stubbing every call to FileUtils or File, you're tightly coupling your tests with the implementation.

def test_creates_directory
  FileUtils.expects(:mkdir).with("directory").once
  Library.add "directory"
end

The above test will break if we decide to use mkdir_p in our code. Refactoring code shouldn't necessitate refactoring tests.

With FakeFS:

def test_creates_directory
  Library.add "directory"
  assert File.directory?("directory")
end

Woot.

require 'fakefs'

# That's it.

require 'fakefs/safe'

FakeFS.activate!
# your code
FakeFS.deactivate!

# or
FakeFS do
  # your code
end

The above approach works with RSpec as well. In addition you may include FakeFS::SpecHelpers to turn FakeFS on and off in a given example group:

require 'fakefs/spec_helpers'

describe "my spec" do
  include FakeFS::SpecHelpers
end

See lib/fakefs/spec_helpers.rb for more info.

FakeFS provides a test suite and works with symlinks. It's also strictly a test-time dependency: your actual library does not need to use or know about FakeFS.

FakeFS internally uses the Pathname and FileUtils constants. If you use these in your app, be certain you're properly requiring them and not counting on FakeFS' own require.

http://gist.github.com/156091

$ gem install fakefs

$ rip install git://github.com/defunkt/fakefs.git

Once you've made your great commits:

1. Fork FakeFS
2. Create a topic branch - git checkout -b my_branch
3. Push to your branch - git push origin my_branch
4. Create an Issue with a link to your branch
5. That's it!

• Code: git clone git://github.com/defunkt/fakefs.git
• Home: http://github.com/defunkt/fakefs
• Docs: http://defunkt.github.com/fakefs
• Bugs: http://github.com/defunkt/fakefs/issues
• List: http://groups.google.com/group/fakefs
• Test: http://runcoderun.com/defunkt/fakefs
• Gems: http://gemcutter.org/gems/fakefs