Fix coverage tracking to load SimpleCov before application code

Extract SimpleCov setup to simplecov_setup.rb and load it via
Minitest's test_prelude so it starts before any application code
regardless of how tests are invoked.

Author: cfis

Rakefile

@@ -5,4 +5,6 @@
 require "bundler/gem_tasks"
 
 require "minitest/test_task"
-Minitest::TestTask.create
+Minitest::TestTask.create do |t|
+  t.test_prelude = 'require "simplecov_setup"'
+end

test/abstract_test.rb

@@ -1,16 +1,5 @@
 require 'bundler/setup'
-
-if ENV['COVERAGE']
-  require 'simplecov'
-  if ENV['CI']
-    require 'simplecov-cobertura'
-    SimpleCov.formatter = SimpleCov::Formatter::CoberturaFormatter
-  end
-  SimpleCov.start do
-    add_filter '/test/'
-    track_files 'lib/**/*.rb'
-  end
-end
+require_relative 'simplecov_setup'
 
 require 'fileutils'
 require 'minitest/autorun'

test/simplecov_setup.rb

@@ -0,0 +1,11 @@
+if ENV['COVERAGE']
+  require 'simplecov'
+  if ENV['CI']
+    require 'simplecov-cobertura'
+    SimpleCov.formatter = SimpleCov::Formatter::CoberturaFormatter
+  end
+  SimpleCov.start do
+    add_filter '/test/'
+    track_files 'lib/**/*.rb'
+  end
+end