Create an lcov file for coverage instead of the automatic simplecov formatter for coveralls

Gemfile

@@ -13,7 +13,11 @@ gem 'rake'
 
 group :test do
   gem 'rspec', '~> 3.0'
-  gem 'coveralls', '~> 0.8.20'
+
+  if Gem.ruby_version >= Gem::Version.new('2.4.0')
+    gem 'simplecov', '~> 0.18'
+    gem 'simplecov-lcov', '~> 0.8'
+  end
 
   gem 'rack', ENV['RACK_VERSION'] ? "~> #{ENV['RACK_VERSION']}" : nil
 end

spec/spec_helper.rb

@@ -6,13 +6,23 @@
 # of the MIT license. See the LICENSE.txt file for details.
 
 if ENV['COVERAGE'].to_s == 'true'
+  if Gem.ruby_version <= Gem::Version.new('2.4.0')
+    STDERR.puts "Simplecov requires Ruby 2.4, but we are currently on " \
+      "#{RUBY_VERSION}. Try running the spec again without collecting " \
+      "coverage details (by leaving the COVERAGE environment variable empty) " \
+      "or by using a newer Ruby version."
+    exit 1
+  end
+
   require 'simplecov'
 
-  if ENV['CI'] == 'true'
-    require 'coveralls'
-    SimpleCov.formatter = SimpleCov::Formatter::MultiFormatter[
+  if ENV['CI'].to_s == 'true'
+    require 'simplecov-lcov'
+
+    SimpleCov::Formatter::LcovFormatter.config.report_with_single_file = true
+    SimpleCov.formatters = [
       SimpleCov::Formatter::HTMLFormatter,
-        Coveralls::SimpleCov::Formatter
+      SimpleCov::Formatter::LcovFormatter
     ]
   else
     SimpleCov.formatter = SimpleCov::Formatter::HTMLFormatter