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fakefs
1.0K Stars 188 Forks MIT License 859 Commits 31 Opened issues

Description

A fake filesystem. Use it in your tests.

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FakeFS build status

Mocking calls to FileUtils or File means tightly coupling tests with the implementation.

it "creates a directory" do
  FileUtils.expects(:mkdir).with("directory").once
  Library.add "directory"
end

The above test will break if

mkdir_p
is used instead. Refactoring code should not necessitate refactoring tests.

A better approach is to use a temp directory if you are working with relative directories.

require 'tmpdir'

it "creates a directory" do Dir.mktmpdir do |dir| Dir.chdir dir do Library.add "directory" assert File.directory?("directory") end end end

But if you are working with absolute directories or do not want to use temporary directories, use FakeFS instead:

it "creates a directory" do
  FakeFS do
    Library.add "directory"
    assert File.directory?("directory")
  end
end

Installation

gem install fakefs

Usage

To fake out the FS:

require 'fakefs'

Temporarily faking the FS

require 'fakefs/safe'

FakeFS.activate!

your code

FakeFS.deactivate!

or

FakeFS do

your code

end

Rails

In rails projects, add this to your Gemfile:

gem "fakefs", require: "fakefs/safe"

RSpec

Include FakeFS::SpecHelpers to turn FakeFS on and off in an example group:

require 'fakefs/spec_helpers'

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

See

lib/fakefs/spec_helpers.rb
for more info.

To use FakeFS within a single test and be guaranteed a fresh fake filesystem: ``` ruby require 'fakefs/safe'

describe "my spec" do context "my context" do it "does something to the filesystem" FakeFS.with_fresh do # whatever it does end end end end ```

FakeFs ---
TypeError: superclass mismatch for class File

pp
and
fakefs
may collide, even if you're not actually explicitly using
pp
. Adding
require 'pp'
before
require 'fakefs'
should fix the problem locally. For a module-level fix, try adding it to the
Gemfile
:
source "https://rubygems.org"

require 'pp'

list of gems

The problem may not be limited to

pp
; any gems that add to
File
may be affected.

Working with existing files

Clone existing directories or files to reuse them during tests, they are safe to modify.

FakeFS do
  config = File.expand_path('../../config', __FILE__)

FakeFS::FileSystem.clone(config) expect(File.read("#{config}/foo.yml")).to include("original-content-of-foo")

File.write("#{config}/foo.yml"), "NEW") expect(File.read("#{config}/foo.yml")).to eq "NEW" end

Integrating with other filesystem libraries

Third-party libraries may add methods to filesystem-related classes. FakeFS doesn't support these methods out of the box, but you can define fake versions yourself on the equivalent FakeFS classes. For example, FileMagic adds

File#content_type
. A fake version can be provided as follows:
FakeFS::File.class_eval do
  def content_type
    'fake/file'
  end
end

Caveats

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.

As of v0.5.0, FakeFS's current working directory (i.e.

Dir.pwd
) is independent of the real working directory. Previously if the real working directory were, for example,
/Users/donovan/Desktop
, then FakeFS would use that as the fake working directory too, even though it most likely didn't exist. This caused all kinds of subtle bugs. Now the default working directory is the only thing that is guaranteed to exist, namely the root (i.e.
/
). This may be important when upgrading from v0.4.x to v0.5.x, especially if you depend on the real working directory while using FakeFS.

FakeFS replaces File and FileUtils, but is not a filesystem replacement, so gems that use strange commands or C might circumvent it. For example, the

sqlite3
gem will completely ignore any faked filesystem.

Speed?

http://gist.github.com/156091

Contributing

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. Open a Pull Request
  5. That's it!

Meta

Releasing

  1. bundle exec rake bump:patch
    or minor/major
  2. bundle exec rake release

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