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Single Cov CI

Actionable code coverage.

rspec spec/foobar_spec.rb
114 example, 0 failures

lib/foobar.rb new uncovered lines introduced (2 current vs 0 configured)
Uncovered lines:
  • Missing coverage on every 💚 test run
  • Catch coverage issues before making PRs
  • Easily add coverage enforcement for legacy apps
  • 2-5% runtime overhead on small files, compared to 20% for SimpleCov
  • Branch coverage (disable via branches: false)
  • Use with forking_test_runner for exact per test coverage
# Gemfile
gem 'single_cov', group: :test

# spec/spec_helper.rb ... load single_cov before rails, libraries, minitest, or rspec
require 'single_cov'
SingleCov.setup :rspec # or :minitest

# spec/foobar_spec.rb ... add covered! call to test files
require 'spec_helper'

describe "xyz" do ...

Missing target file

Each covered! call expects to find a matching file, if it does not:

# change all guessed paths
SingleCov.rewrite { |f| f.sub('lib/unit/', 'app/models/') }

# mark directory as being in app and not lib
SingleCov::RAILS_APP_FOLDERS << 'presenters'

# add 1-off
SingleCov.covered! file: 'scripts/weird_thing.rb'

Known uncovered

Add the inline comment # uncovered to ignore uncovered code.

Prevent addition of new uncovered code, without having to cover all existing code by marking how many lines are uncovered:

SingleCov.covered! uncovered: 4

Making a folder not get prefixed with lib/

For example packwerk components are hosted in public and not lib/public

SingleCov::PREFIXES_TO_IGNORE << "public"

Missing coverage for implicit else in if or case statements

When a report shows for example 1:14-16 # else, that indicates that the implicit else is not covered.

# needs 2 tests: one for `true` and one for `false`
raise if a == b

# needs 2 tests: one for `when b` and one for `else`
case a
when b

Verify all code has tests & coverage

# spec/coverage_spec.rb
SingleCov.not_covered! # not testing any code in lib/

describe "Coverage" do
  # recommended
  it "does not allow new tests without coverage check" do
    # option :tests to pass custom Dir.glob results

  # recommended
  it "does not allow new untested files" do
    # option :tests and :files to pass custom Dir.glob results
    # :untested to get it passing with known untested files
  # optional for full coverage enforcement
  it "does not reduce full coverage" do
    # make sure that nobody adds `uncovered: 123` to any test that did not have it before
    # option :tests to pass custom Dir.glob results
    # option :currently_complete for expected list of full covered tests
    # option :location for if you store that list in a separate file
    SingleCov.assert_full_coverage currently_complete: ["test/a_test.rb"]

Automatic bootstrap

Run this from irb to get SingleCov added to all test files.

tests = Dir['spec/**/*_spec.rb']
command = "bundle exec rspec %{file}"

tests.each do |f|
  content =
  next if content.include?('SingleCov.')

  # add initial SingleCov call
  content = content.split(/\n/, -1)
  insert = content.index { |l| l !~ /require/ && l !~ /^#/ }
  content[insert...insert] = ["", "SingleCov.covered!"]
  File.write(f, content.join("\n"))

  # run the test to check coverage
  result = `#{command.sub('%{file}', f)} 2>&1`
  if $?.success?
    puts "#{f} is good!"

  if uncovered = result[/\((\d+) current/, 1]
    # configure uncovered
    puts "Uncovered for #{f} is #{uncovered}"
    content[insert+1] = "SingleCov.covered! uncovered: #{uncovered}"
    File.write(f, content.join("\n"))
    # mark bad tests for manual cleanup
    content[insert+1] = "# SingleCov.covered! # TODO: manually fix this"
    File.write(f, content.join("\n"))
    puts "Manually fix: #{f} ... output is:\n#{result}"

Cover multiple files from a single test

When a single integration test covers multiple source files.

SingleCov.covered! file: 'app/modes/user.rb'
SingleCov.covered! file: 'app/mailers/user_mailer.rb'
SingleCov.covered! file: 'app/controllers/user_controller.rb'

Generating a coverage report

SingleCov.coverage_report = "coverage/.resultset.json"
SingleCov.coverage_report_lines = true # only report line coverage for coverage systems that do not support branch coverage


Michael Grosser
License: MIT