Add spec

Author: dduugg

Library/Homebrew/test/rubocop_spec.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require "open3"
+require "yaml"
 
 RSpec.describe "RuboCop" do
   context "when calling `rubocop` outside of the Homebrew environment" do
@@ -23,4 +24,17 @@
       expect(status).to be_a_success
     end
   end
+
+  describe "configuration" do
+    it "has TargetRubyVersion matching .ruby-version" do
+      rubocop_config_path = HOMEBREW_LIBRARY_PATH.parent/".rubocop.yml"
+      rubocop_config = YAML.unsafe_load_file(rubocop_config_path)
+      target_ruby_version = rubocop_config.dig("AllCops", "TargetRubyVersion")
+
+      ruby_version_path = HOMEBREW_LIBRARY_PATH/".ruby-version"
+      ruby_version = ruby_version_path.read.strip.to_f
+
+      expect(target_ruby_version).to eq(ruby_version)
+    end
+  end
 end