test: add instance variable comments.

Library/Homebrew/test/download_strategies/git_spec.rb

@@ -18,8 +18,11 @@ describe GitDownloadStrategy do
 
   def git_commit_all
     system "git", "add", "--all"
-    system "git", "commit", "-m", "commit number #{@commit_id}" # rubocop:disable RSpec/InstanceVariable
+    # Allow instance variables here to have nice commit messages.
+    # rubocop:disable RSpec/InstanceVariable
+    system "git", "commit", "-m", "commit number #{@commit_id}"
     @commit_id += 1
+    # rubocop:enable RSpec/InstanceVariable
   end
 
   def setup_git_repo

Library/Homebrew/test/support/helper/spec/shared_context/integration_test.rb

@@ -119,7 +119,10 @@ RSpec.shared_context "integration test" do # rubocop:disable RSpec/ContextWordin
     end
 
     Bundler.with_unbundled_env do
-      stdout, stderr, status = Open3.capture3(env, *@ruby_args, *args) # rubocop:disable RSpec/InstanceVariable
+      # Allow instance variable here to improve performance through memoization.
+      # rubocop:disable RSpec/InstanceVariable
+      stdout, stderr, status = Open3.capture3(env, *@ruby_args, *args)
+      # rubocop:enable RSpec/InstanceVariable
       $stdout.print stdout
       $stderr.print stderr
       status

Library/Homebrew/test/utils/git_spec.rb

@@ -45,6 +45,7 @@ describe Utils::Git do
   end
 
   let(:file) { "README.md" }
+  # Allow instance variables here for a simpler `before do` block.
   # rubocop:disable RSpec/InstanceVariable
   let(:file_hash1) { @h1[0..6] }
   let(:file_hash2) { @h2[0..6] }