Add test for SystemCommand with SIGINT handler.

Library/Homebrew/test/spec_helper.rb

@@ -165,12 +165,14 @@ RSpec.configure do |config|
 
   config.around do |example|
     def find_files
+      return [] unless File.exist?(TEST_TMPDIR)
+
       Find.find(TEST_TMPDIR)
           .reject { |f| File.basename(f) == ".DS_Store" }
+          .reject { |f| TEST_DIRECTORIES.include?(Pathname(f)) }
           .map { |f| f.sub(TEST_TMPDIR, "") }
     end
 
-    begin
     Homebrew.raise_deprecation_exceptions = true
 
     Formulary.clear_cache
@@ -193,6 +195,7 @@ RSpec.configure do |config|
     @__stdout = $stdout.clone
     @__stderr = $stderr.clone
 
+    begin
       if (example.metadata.keys & [:focus, :byebug]).empty? && !ENV.key?("VERBOSE_TESTS")
         $stdout.reopen(File::NULL)
         $stderr.reopen(File::NULL)
@@ -224,7 +227,7 @@ RSpec.configure do |config|
       Tab.clear_cache
 
       FileUtils.rm_rf [
-        TEST_DIRECTORIES.map(&:children),
+        *TEST_DIRECTORIES,
         *Keg::MUST_EXIST_SUBDIRECTORIES,
         HOMEBREW_LINKED_KEGS,
         HOMEBREW_PINNED_KEGS,

Library/Homebrew/test/system_command_spec.rb

@@ -281,5 +281,28 @@ describe SystemCommand do
         }.to raise_error.with_message(redacted_msg).and output(redacted_msg).to_stderr
       end
     end
+
+    context "when a `SIGINT` handler is set in the parent process" do
+      it "is not interrupted" do
+        start_time = Time.now
+
+        pid = fork do
+          trap("INT") do
+            # Ignore SIGINT.
+          end
+
+          described_class.run! "sleep", args: [5]
+
+          exit!
+        end
+
+        sleep 1
+        Process.kill("INT", pid)
+
+        Process.waitpid(pid)
+
+        expect(Time.now - start_time).to be >= 5
+      end
+    end
   end
 end