fake your files - memfs

Fake your filesSimon Courtois - @happynoff

How to test files manipulation ?

it "creates the given file" do

endfile_maker.create('thing.txt')

class FileMaker def create(path) FileUtils.touch(path) end end

it "creates the given file" do

endexpect(File.exists?(‘thing.txt’)).to be_truefile_maker.create('thing.txt')

class FileMaker def create(path) FileUtils.touch(path) end end

class FileMaker def create(path) FileUtils.touch(path) end end

it "creates the given file" do

end

file_maker.create('thing.txt')FileUtils.rm('thing.txt')

expect(File.exists?(‘thing.txt’)).to be_true

Read-only file system ?

it "creates the given file" do

endfile_maker.create('thing.txt')

class FileMaker def create(path) FileUtils.touch(path) end end

class FileMaker def create(path) FileUtils.touch(path) end end

it "creates the given file" do

end

expect(FileUtils).to receive(:touch) .with(‘thing.txt') .and_return(true)file_maker.create('thing.txt')

Boooh! Test behavior not implementation

Enters a solution FakeFS

it "creates the given file" dofile_maker.create('thing.txt')

end expect(File.exists?('thing.txt')).to be_true

class FileMaker def create(path) FileUtils.touch(path end end

)

class FileMaker def create(path) FileUtils.touch(path end end

it "creates the given file" doFakeFS do

file_maker.create('thing.txt')expect(File.exists?('thing.txt')).to

endend

be_true

)

class FileMaker def create(path) FileUtils.touch(path end end

it "creates the given file" doFakeFS do

file_maker.create('thing.txt')expect(File.exists?('thing.txt')).to

endend

be_false

, noop: true)

be_true

BOOM! That’s a red dot

FakeFS overwrites FileUtils and

ignores options

Try MemFS

class FileMaker def create(path) FileUtils.touch(path, noop: true) end end

it "creates the given file" dofile_maker.create('thing.txt')expect(File.exists?('thing.txt')).to be_false

end

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

endend

MemFs.activate do

MemFs doesn’t overwrite FileUtils

only low-level classes

File.open('thing.txt') do |f| f.puts 'hello' end !File.read('thing.txt') # => "hello\n"

File.symlink('thing.txt', 'thing-link.txt') File.symlink?('thing-link.txt') # => true

File.chmod(0777, 'thing.txt')

File.stat('thing.txt').ctime # => 2014-02-04 19:00:00 +0100

Some resources

http://github.com/defunkt/fakefs

http://github.com/simonc/memfs

Questions?

Thank youSimon Courtois - @happynoff