Cucumber::Blanket

Works to extract accumulated Blanket.js coverage data from the browser from a Cucumber environment. Accumulated, in this context, means that coverage data is accumulated from scenario to scenario, in an additive fashion.

Add this line to your application's Gemfile:

gem 'cucumber-blanket'

And then execute:

$ bundle

Or install it yourself as:

$ gem install cucumber-blanket

You should be using Cucumber

Require this gem at the top of features/support/env.rb or before using it.

require 'cucumber/blanket'

Install blanket.js

Two javascript files are bundled;

• blanket.js -- the library itself
• cucumber-blanket.js -- a very simple modification

These two files must be loaded on the front-end --- be sure to follow blanket.js's specifications (you must add the attribute data-cover to any scripts you want blanket.js to instrument)

cucumber-blanket.js initiates a coverage report session -- you are expected to complete the session from the Cucumber side. In this design, we make use of Cucumber's After hook:

After do |scenario|
  # Grab code coverage from the frontend
  # Currently this adds >1 second to every scenario, but it's worth it
  Cucumber::Blanket.extract_from page
end

Of course every scenario will touch on different parts of your code, as such Cucumber::Blanket OR's the lines. In other words, if line 10 of File A was covered in Scenario X, but not in Scenario Y, line 10 is considered covered when Cucumber has finished running.

Finally, to gain access to the accumulated coverage data, you can use the shorthand Cucumber::Blanket.files:

after_exit do
  covdata =  # do something with it
  File.open("tmp/coverage.json", "w") do |file|
    file.write Cucumber::Blanket.files.to_json
    # writes out JSON of this form of ruby hash:
    # => {"http://127.0.0.1:32344/js/collections/assets.js"=>
    #  [3, 3, 3, nil, 3, nil, nil, nil, 0, 0, nil, 0, nil, nil, nil, nil, 0, 0]}
    # {filename=>[lineCov,lineCov,lineCov]}
    # At this stage you can fetch the files and create a nice HTML report, etc
  end
end

I have both of these in my features/support/hooks.rb file. As far as doing something useful with the coverage data, that's left up to the user, another gem, or maybe blanket.js itself from Node.js.

You can use Cucumber::Blanket.percent to get a float value of coverage of known lines of code.

For example, you can do something like this to watch coverage increasing on every scenario:

After do |scenario|
  old_pct = Cucumber::Blanket.percent
  Cucumber::Blanket.extract_from page
  current_pct = Cucumber::Blanket.percent
  pct_added = current_pct - old_pct
  STDOUT.puts "Coverage: #{current_pct}% (+#{pct_added}%)"
end

at_exit do
  STDOUT.puts "Final coverage: #{Cucumber::Blanket.percent}%"
end

After you've captured some coverage data, you can create an HTML report like so:

Cucumber::Blanket.write_html_report File.join(File.dirname(__FILE__), '../../coverage.html')

I like to put this in after_exit in my Cucumber hooks.rb file

To create the spec/fixtures/simple.json with new real data, add this line to Cucumber::Blanket#extract_from once you have a handle to page_data:

File.open("tmp/out.json", 'w'){|f| f.write page_data.to_json}

Run it through jsbeautifier and add it

Run the specs with the environment variable showreport set. e.g. showreport=1 bundle exec rspec spec

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