My talk for Paris.rb on 2014-02-04.

1. Fake your files
Simon Courtois - @happynoff

2. How to test files
manipulation ?

3. class FileMaker
def create(path)
FileUtils.touch(path)
end
end
it "creates the given file" do
file_maker.create('thing.txt')
end

4. class FileMaker
def create(path)
FileUtils.touch(path)
end
end
it "creates the given file" do
file_maker.create('thing.txt')
expect(File.exists?(‘thing.txt’)).to be_true
end

5. class FileMaker
def create(path)
FileUtils.touch(path)
end
end
it "creates the given file" do
FileUtils.rm('thing.txt')
file_maker.create('thing.txt')
expect(File.exists?(‘thing.txt’)).to be_true
end

6. Read-only file system ?

7. class FileMaker
def create(path)
FileUtils.touch(path)
end
end
it "creates the given file" do
file_maker.create('thing.txt')
end

8. class FileMaker
def create(path)
FileUtils.touch(path)
end
end
it "creates the given file" do
expect(FileUtils).to receive(:touch)
.with(‘thing.txt')
.and_return(true)
file_maker.create('thing.txt')
end

9. Boooh!
Test behavior not
implementation

10. Enters a solution
FakeFS

11. class FileMaker
def create(path)
FileUtils.touch(path)
end
end
it "creates the given file" do
file_maker.create('thing.txt')
expect(File.exists?('thing.txt')).to be_true
end

12. class FileMaker
def create(path)
FileUtils.touch(path)
end
end
it "creates the given file" do
FakeFS do
file_maker.create('thing.txt')
expect(File.exists?('thing.txt')).to be_true
end
end

13. class FileMaker
def create(path)
FileUtils.touch(path, noop: true)
end
end
it "creates the given file" do
FakeFS do
file_maker.create('thing.txt')
expect(File.exists?('thing.txt')).to be_true
be_false
end
end

14. BOOM!
That’s a red dot

15. FakeFS
overwrites FileUtils and
ignores options

16. Try MemFS

17. class FileMaker
def create(path)
FileUtils.touch(path, noop: true)
end
end
it "creates the given file" do
file_maker.create('thing.txt')
expect(File.exists?('thing.txt')).to be_false
end

18. class FileMaker
def create(path)
FileUtils.touch(path, noop: true)
end
end
it "creates the given file" do
MemFs.activate do
file_maker.create('thing.txt')
expect(File.exists?('thing.txt')).to be_false
end
end

19. MemFs
doesn’t overwrite FileUtils
only low-level classes

20. File.open('thing.txt') do |f|
f.puts 'hello'
end
!
File.read('thing.txt')
# => "hellon"
File.symlink('thing.txt', 'thing-link.txt')
File.symlink?('thing-link.txt')
# => true
File.stat('thing.txt').ctime
# => 2014-02-04 19:00:00 +0100
File.chmod(0777, 'thing.txt')

21. Some resources

22. http://github.com/defunkt/fakefs
http://github.com/simonc/memfs

23. Questions
?

24. Thank you
Simon Courtois - @happynoff