Add rescue and test for child_process terminate method

Author: aguspe

rb/lib/selenium/webdriver/common/child_process.rb

@@ -122,6 +122,8 @@ def terminate_and_wait_else_kill(timeout)
 
       def terminate(pid)
         Process.kill(SIGTERM, pid)
+      rescue Errno::ECHILD, Errno::ESRCH
+        # Process does not exist, nothing to terminate
       end
 
       def kill(pid)

rb/spec/unit/selenium/webdriver/common/child_process_spec.rb

@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+# Licensed to the Software Freedom Conservancy (SFC) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The SFC licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+require File.expand_path('../spec_helper', __dir__)
+
+module Selenium
+  module WebDriver
+    describe ChildProcess do
+      it 'does not raise an error when terminating a killed process' do
+        process = described_class.new('sleep', '5')
+        process.start
+
+        pid = process.instance_variable_get(:@pid)
+        Process.kill('KILL', pid)
+
+        expect {
+          process.send(:terminate, pid)
+        }.not_to raise_error
+      end
+    end
+  end
+end