Add test coverage using test_cov rake task

Currently: 3352 / 3602 LOC (93.06%) covered

2 files changed, 20 insertions, 0 deletions

diff --git a/Rakefile b/Rakefile
index 3a232cc5..6ad8d1f0 100644
--- a/Rakefile
+++ b/Rakefile
@@ -92,6 +92,12 @@ Rake::TestTask.new("test:regular") do |t|
   t.verbose = true
 end
 
+desc "Run tests with coverage"
+task "test_cov" do
+  ENV['COVERAGE'] = '1'
+  Rake::Task['test:regular'].invoke
+end
+
 desc "Run all the fast + platform agnostic tests"
 task test: %w[spec test:regular]
 
diff --git a/test/helper.rb b/test/helper.rb
index 7e43aa8a..c13a71f0 100644
--- a/test/helper.rb
+++ b/test/helper.rb
@@ -1,5 +1,19 @@
 # frozen_string_literal: true
 
+if ENV.delete('COVERAGE')
+  require 'coverage'
+  require 'simplecov'
+
+  def SimpleCov.rack_coverage(**opts)
+    start do
+      add_filter "/test/"
+      add_group('Missing'){|src| src.covered_percent < 100}
+      add_group('Covered'){|src| src.covered_percent == 100}
+    end
+  end
+  SimpleCov.rack_coverage
+end
+
 $:.unshift(File.expand_path('../lib', __dir__))
 require_relative '../lib/rack'
 require 'minitest/global_expectations/autorun'