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 people, the answer is yes, the joke in the name is intended ;)
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
While FakeFS is pretty cool it overrides classes like FileUtils
. This kind of override is problematic when you rely on real behavior from this kind of tool.
For instance, trying to test the following with FakeFS will not work, the noop
option will be ignored:
FileUtils.touch('somefile.txt', noop: true)
MemFs tries to be compliant with the Ruby API by overriding only the low level classes (C classes) like File, Dir or File::Stat leaving the stdlib classes untouched and still working, being less intrusive that way.
Some stdlib classes may be overriden at some point if they don't use File
or Dir
, like Pathname
, etc.
Another key point is that MemFs aims to implement every single method provided by Ruby classes (when possible) and to behave and return exactly the same way as the original classes.
Add this line to your application's Gemfile:
gem 'memfs'
And then execute:
$ bundle
Or install it yourself as:
$ gem install memfs
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
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
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
- Ruby 1.9.3 or newer
- MemFs doesn't implement IO so methods like
FileUtils.copy_stream
andIO.write
are still the originals. - Similarly, MemFs doesn't implement Kernel, so don't use a naked
open()
call. This uses theKernel
class viamethod_missing
, which MemFs will not intercept. - Pipes and Sockets are not handled for now.
require "pp"
will raise a superclass mismatch exception since MemFs::File does not inherit from IO. The best thing to do is to require pp before MemFs.
- Implement missing methods from
File
,Dir
andStat
- 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