Support for rspecs running in parallel on different workers

[Nishant Arora]

When splitting rspec across multiple workers using something like knapsack, what would be the best way to club all generated coverage reports into a single artifact?

[Jan Grodowski]

Hey @whizzzkid! Here's an example from https://undercover-ci.com/docs#parallel-tests. It uses SimpleCov.collate also described in the SimpleCov documentation.

#!/usr/bin/env ruby
# frozen_string_literal: true

require 'simplecov'
require 'simplecov-lcov'

puts('Merging coverage results from parallel CircleCI tests containers into a single LCOV report...')

SimpleCov.collate(Dir['/home/circleci/rspec/*.resultset.json']) do
  enable_coverage(:branch)
end

report_path = ARGV[0] || 'coverage.lcov'
SimpleCov.formatter = SimpleCov::Formatter::LcovFormatter
SimpleCov::Formatter::LcovFormatter.config.report_with_single_file = true
SimpleCov::Formatter::LcovFormatter.config.single_report_path = report_path

merged_result = SimpleCov.result
merged_result.format!

if File.size(report_path).zero?
  puts('Written report has 0 bytes')
  exit 1
end
puts("Done! LCOV saved to #{SimpleCov::Formatter::LcovFormatter.config.single_report_path}")

Depending on which CI you use, you'd need a script like this to run after all the workers have finished and then feed the merged coverage report to undercover.

Let me know how it goes!