Make sure no error is raised when a process is already terminated (#939)

lib/parallel_tests.rb

@@ -44,6 +44,8 @@ def pid_file_path
 
     def stop_all_processes
       pids.all.each { |pid| Process.kill(:INT, pid) }
+    rescue Errno::ESRCH
+      # Process already terminated, do nothing
     end
 
     # copied from http://github.com/carlhuda/bundler Bundler::SharedHelpers#find_gemfile

spec/parallel_tests_spec.rb

@@ -194,6 +194,13 @@ def with_running_processes(count, wait = 0.2)
         expect(ParallelTests.pids.count).to eq(0)
       end
     end
+
+    it "doesn't fail if the pid has already been killed", unless: Gem.win_platform? do
+      ParallelTests.with_pid_file do
+        ParallelTests.pids.add(1234)
+        expect { ParallelTests.stop_all_processes }.not_to raise_error
+      end
+    end
   end
 
   it "has a version" do