MemFs

MemFs is an in-memory filesystem that can be used for your tests.

When you're writing code that manipulates files, directories, symlinks, you need to be able to test it without touching your hard drive. MemFs is made for it.

MemFs is intended for tests but you can use it for any other scenario needing in memory file system.

MemFs is greatly inspired by the awesome FakeFs.

The main goal of MemFs is to be 100% compatible with the Ruby libraries like FileUtils.

For french guys, the answer is yes, the joke in the name is intended ;)

Take a look

Here is a simple example of MemFs usage:

MemFs.activate!
File.open('/test-file', 'w') { |f| f.puts "hello world" }
File.read('/test-file') #=> "hello world\n"
MemFs.deactivate!

File.exists?('/test-file') #=> false

# Or with the block syntax

MemFs.activate do
  FileUtils.touch('/test-file', verbose: true, noop: true)
  File.exists?('/test-file') #=> true
end

File.exists?('/test-file') #=> false

Installation

Add this line to your application's Gemfile:

gem 'memfs'

And then execute:

$ bundle

Or install it yourself as:

$ gem install memfs

Usage in tests

Global activation

Add the following to your spec_helper.rb:

RSpec.configure do |config|
  config.before do
    MemFs.activate!
  end

  config.after do
    MemFs.deactivate!
  end
end

All the spec will be sandboxed in MemFs.

If you want to set it globally with flag activation, you can do the following in you spec_helper.rb file:

Rspec.configure do |c|
  c.around(:each, memfs: true) do |example|
  MemFs.activate { example.run }
  end
end

And then write your specs like this:

it "creates a file", memfs: true do
  subject.create_file('test.rb')
  expect(File.exists?('test.rb')).to be_true
end

Local activation

You can choose to activate MemFs only for a specific test:

describe FileCreator do
  describe '.create_file' do
    it "creates a file" do
      MemFs.activate do
        subject.create_file('test.rb')
        expect(File.exists?('test.rb')).to be_true
      end
    end
  end
end

No real file will be created during the test.

You can also use it for a specific describe block:

describe FileCreator do
  before { MemFs.activate! }
  after { MemFs.deactivate! }

  describe '.create_file' do
    it "creates a file" do
      subject.create_file('test.rb')
      expect(File.exists?('test.rb')).to be_true
    end
  end
end

Utilities

You can use MemFs.touch to quickly create a file and its parent directories:

MemFs.activate do
  MemFs.touch('/path/to/some/file.rb')
  File.exist?('/path/to/some/file.rb') # => true
end

Requirements

Ruby 2.0+

Known issues

MemFs doesn't implement IO so FileUtils.copy_stream is still the original one
Pipes and Sockets are not handled for now

TODO

Implement missing methods from File, Dir and Stat

Contributing

Fork it
Create your feature branch (git checkout -b my-new-feature)
Commit your changes (git commit -am 'Add some feature')
Push to the branch (git push origin my-new-feature)
Create new Pull Request