Handle signal-terminated processes in exit status

When a child process is terminated by a Unix signal (e.g., SIGKILL,
SIGTERM), $?.exitstatus returns nil. This caused downstream code to
break when comparing exit statuses.

Following Unix shell convention, signal terminations now return
128 + signal_number (e.g., 137 for SIGKILL, 143 for SIGTERM).

Falls back to exit status 1 if neither exitstatus nor termsig is
available.

Author: bazlo

lib/parallel_tests/test/runner.rb

@@ -110,7 +110,16 @@ def execute_command_and_capture_output(env, cmd, options)
             capture_output(io, env, options)
           end
           ParallelTests.pids.delete(pid) if pid
-          exitstatus = $?.exitstatus
+
+          status = $?
+          exitstatus = if status.exitstatus
+            status.exitstatus
+          elsif status.termsig
+            status.termsig + 128
+          else
+            1
+          end
+
           seed = output[/seed (\d+)/, 1]
 
           output = "#{Shellwords.shelljoin(cmd)}\n#{output}" if report_process_command?(options) && options[:serialize_stdout]

spec/parallel_tests/test/runner_spec.rb

@@ -564,6 +564,13 @@ def run_with_file(content)
       end
     end
 
+    it "returns exit status 128 + signal number when terminated by signal", unless: Gem.win_platform? do
+      run_with_file("Process.kill('KILL', Process.pid)") do |path|
+        result = call(["ruby", path], 1, 4, {})
+        expect(result[:exit_status]).to eq 128 + 9 # SIGKILL = 9
+      end
+    end
+
     it "prints each stream to the correct stream" do
       skip "open3"
       _out, err = run_with_file("puts 123 ; $stderr.puts 345 ; exit 5") do |path|