danmayer / coverband翻译 / 编辑






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Key FeaturesInstallationCoverage ReportVerify Correct InstallationAdvanced ConfigLicenseChange Log / Roadmap

A gem to measure production code usage, showing a counter for the number of times each line of code that is executed. Coverband allows easy configuration to collect and report on production code usage. It reports in the background via a thread or can be used as Rack middleware, or manually configured to meet any need.

Note: Coverband is not intended for test code coverage, for that we recommended using SimpleCov.

Key Features

The primary goal of Coverband is giving deep insight into your production runtime usage of your application code, while having the least impact on performance possible.

  • Low performance overhead
  • Very simple setup and configuration
  • Out of the box support for all standard code execution paths (web, cron, background jobs, rake tasks, etc)
  • Easy to understand actionable insights from the report
  • Development mode, offers deep insight of code usage details (number of LOC execution during single request, etc) during development.
  • Mountable web interface to easily share reports



Coverband stores coverage data in Redis. The Redis endpoint is looked for in this order:

  3. localhost

The redis store can also be explicitly defined within the coverband.rb. See advanced config.

Gem Installation

Add this line to your application's Gemfile, remember to bundle install after updating:

gem 'coverband'

If tracking gem usage, be sure to include coverband before other gems you would like to track.


The Railtie integration means you shouldn't need to do anything anything else other than ensure coverband is required after rails within your Gemfile.


For the best coverage you want this loaded as early as possible. I have been putting it directly in my config.ru but you could use an initializer, though you may end up missing some boot up coverage. To start collection require Coverband as early as possible.

require 'coverband'
require File.dirname(__FILE__) + '/config/environment'

use Coverband::Middleware
run ActionController::Dispatcher.new

Coverage Report

Coverband comes with a mountable rack app for viewing reports. For Rails this can be done in config/routes.rb with:

Rails.application.routes.draw do
  mount Coverband::Reporters::Web.new, at: '/coverage'

But don't forget to protect your source code with proper authentication. Something like this when using devise:

Rails.application.routes.draw do
  authenticate :user, lambda { |u| u.admin? } do
    mount Coverband::Reporters::Web.new, at: '/coverage'

Coverband Web Endpoint

The web endpoint is a barebones endpoint that you can either expose direct (after authentication) or you can just link to the actions you wish to expose. The index is intended as a example to showcase all the features.


The web index as available on the Coverband Demo site

  • force coverage collection: This triggers coverage collection on the current webserver process
  • reload Coverband files: This has Coverband reload files as configured (force reload of some files that might not capture Coverage on boot). This can be used to reload files on demand.
  • clear coverage report: This will clear the coverage data. This wipes out all collected data (dangerous)

Rake Tasks

The rake task generates a report locally and opens a browser pointing to coverage/index.html.

rake coverband:coverage

This is mostly useful in your local development environment.

Example Output

Since Coverband is Simplecov output compatible it should work with any of the SimpleCov::Formatter's available. The output below is produced using the default Simplecov HTML formatter.

Index Page image

Details on an example Sinatra app image

Verify Correct Installation

  • boot up your application
  • run app and hit a controller (via a web request, at least one request must complete)
  • run rake coverband:coverage this will show app initialization coverage
  • make another request, or enough that your reporting frequency will trigger
  • run rake coverband:coverage and you should see coverage increasing for the endpoints you hit.

Coverband Demo

Take Coverband for a spin on the live Heroku deployed Coverband Demo. The full source code for the demo is available to help with installation, configuration, and understanding of basic usage.

Example apps

Advanced Config

If you need to configure coverband, this can be done by creating a config/coverband.rb file relative to your project root.

  • See lib/coverband/configuration.rb for all options
  • By default Coverband will try to stored data to Redis
    • Redis endpoint is looked for in this order: ENV['COVERBAND_REDIS_URL'], ENV['REDIS_URL'], or localhost

Below is an example config file for a Rails 5 app:

Coverband.configure do |config|
  config.store = Coverband::Adapters::RedisStore.new(Redis.new(url: ENV['MY_REDIS_URL']))
  config.logger = Rails.logger
  # configure S3 integration
  config.s3_bucket = 'coverband-demo'
  config.s3_region = 'us-east-1'
  config.s3_access_key_id = ENV['AWS_ACCESS_KEY_ID']
  config.s3_secret_access_key = ENV['AWS_SECRET_ACCESS_KEY']

  # config options false, true, or 'debug'. Always use false in production
  # true and debug can give helpful and interesting code usage information
  # they both increase the performance overhead of the gem a little.
  # they can also help with initially debugging the installation.
  config.verbose = false

Ignoring Files

Sometimes you have files that are known to be valuable perhaps in other environments or something that is just run very infrequently. Opposed to having to mentally filter them out of the report, you can just have them ignored in the Coverband reporting by using config.ignore as shown below. Ignore takes a string but can also match with regex rules see how below ignores all rake tasks as an example.

config.ignore =	['config/application.rb',

Writing Coverband Results to S3

If you add some additional Coverband configuration your coverage html report will be written directly to S3, update config/coverband.rb like below.

  # configure S3 integration
  config.s3_bucket = 'coverband-demo'
  config.s3_region = 'us-east-1'
  config.s3_access_key_id = ENV['AWS_ACCESS_KEY_ID']
  config.s3_secret_access_key = ENV['AWS_SECRET_ACCESS_KEY']

Alternatively, Coverband if you don't set via the config.s3_* accessor methods will look for the standard S3 environment variables.


Coverage Data Migration

Between the release of 4.0 and 4.1 our data format changed. This resets all your coverage data. If you want to restore your previous coverage data, feel free to migrate.

rake coverband:migrate

  • We will be working to support migrations going forward, when possible

Clear Coverage

Now that Coverband uses MD5 hashes there should be no reason to manually clear coverage unless one is testing, changing versions, possibly debugging Coverband itself.

rake coverband:clear

Adding Rake Tasks outside of Rails

Rails apps should automaticallly include the tasks via the Railtie.

For non Rails apps, either add the below to your Rakefile or to a file included in your Rakefile such as lib/tasks/coverband.rake if you want to break it up that way.

require 'coverband'
require 'coverband/utils/tasks'

Verify it works

rake -T coverband
rake coverband:clear         # reset coverband coverage data
rake coverband:coverage      # report runtime coverband code coverage

Forcing Coverband to Track Coverage on files loaded during boot safe_reload_files

Coverband will report code usage for anything required or loaded after calling Coverband.start which happens automatically when coverband is required. This means some of the files loaded before coverband such as the Rails application.rb will be reported as having no coverage.

The safe_reload_files reload option in the configuration options can help to ensure you can track any files regardless of loading before Coverband. For example if I wanted to show the coverage of config/coverband.rb, which has to be loaded before calling Coverband.start, I could do that by adding that path to the safe_reload_files option.

Coverband.configure do |config|
  # ... a bunch of other options
  # using the new safe reload to enforce files loaded
  config.safe_reload_files = ['config/coverband.rb']

By adding any files above you will get reporting on those files as part of your coverage runtime report. The files are reloaded when Coverband first starts, you can also trigger a reload via the web interface.

Collecting Gem / Library Usage

Gem usage can be tracked by enabling the track_gems config.

Coverband.configure do |config|
  config.track_gems = true

The track_gems feature exposes a Gems tab in the report which prints out the percentage usage of each Gem. See demo here.

When tracking gems, it is important that Coverband#start is called before the gems to be tracked are required. Since Coverband#start is automatically called by default when coverband is required, list coverband before the other gems to be tracked within your Gemfile. The exception to this are gems like rails and resque. Since coverband has some specific intergrations for these frameworks, these two gems should be required first.

The track_gems config only exposes the overall usage of a gem. In order to see the detail of each file, enable the gem_details flag.

Coverband.configure do |config|
  config.track_gems = true
  config.gem_details = true

This flag exposes line by line usage of gem files. Unfortunately due to the way the coverband report is currently rendered, enabling gem_details slows down viewing of the coverage report in the browser and is not yet recommended.

Manually Starting Coverband

Coverband starts on require of the the library which is usually done within the Gemfile. This can be disabled by setting the COVERBAND_DISABLE_AUTO_START environment variable. This environment variable can be useful to toggle coverband on and off in certain environments.

In order to start coverband manually yourself when this flag is enabled, call Coverband.configure followed by Coverband.start.


Verbose Debug / Development Mode

Note: To debug issues getting Coverband working. I recommend running in development mode, by turning verbose logging on config.verbose = true and passing in the Rails.logger config.logger = Rails.logger to the Coverband config. This makes it easy to follow in development mode. Be careful to not leave these on in production as they will affect performance.

If you are trying to debug locally wondering what code is being run during a request. The verbose modes config.verbose = true and config.verbose = 'debug' can be useful. With true set it will output the number of lines executed per file, to the passed in log. The files are sorted from least used file to most active file. I have even run that mode in production without much of a problem. The debug verbose mode outputs both file usage and provides the number of calls per line of code. For example if you see something like below which indicates that the application_helper has 43150 lines executed. That might seem odd. Then looking at the breakdown of application_helper we can see that line 516 was executed 38,577 times. That seems bad, and is likely worth investigating perhaps memoizing or cacheing is required.

config.verbose = 'debug'

coverband file usage:
  [["/Users/danmayer/projects/app_name/lib/facebook.rb", 6],
  ["/Users/danmayer/projects/app_name/app/models/some_modules.rb", 9],
  ["/Users/danmayer/projects/app_name/app/models/user.rb", 2606],

  /Users/danmayer/projects/app_name/app/helpers/application_helper.rb =>
  [[448, 1], [202, 1],
 [517, 1617], [516, 38577]]


  • Coverband 3.0.X+ requires Ruby 2.3+
  • Coverband currently requires Redis for production usage

Contributing To Coverband

If you are working on adding features, PRs, or bugfixes to Coverband this section should help get you going.

  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. Make sure all tests are passing (run bundle install, make sure Redis is running, and then execute rake test)
  6. Create new Pull Request

Tests & Benchmarks

If you submit a change please make sure the tests and benchmarks are passing.

  • run tests:
    • bundle exec rake
    • BUNDLE_GEMFILE=Gemfile.rails4 bundle exec rake (Same tests using rails 4 instead of 5)
  • view test coverage: open coverage/index.html
  • run the benchmarks before and after your change to see impact
    • rake benchmarks

Known Issues

  • total fail on front end code, because of the precompiled template step basically coverage doesn't work well for erb, slim, and the like.
    • related it will try to report something, but the line numbers reported for ERB files are often off and aren't considered useful. I recommend filtering out .erb using the config.ignore option. The default configuration excludes these files
  • coverage doesn't show for Rails config/application.rb or config/boot.rb as they get loaded when loading the Rake environment prior to starting the Coverage library. See reload files section.

Debugging Redis Store

What files have been synced to Redis?


What is the coverage data in Redis?



This is a MIT License project... See the file license.txt for copying permission.