Check config file existence

lib/sidekiq/cli.rb

@@ -293,6 +293,10 @@ def validate!
         die(1)
       end
 
+      if options[:config_file] && !File.exist?(options[:config_file])
+        raise ArgumentError, "No such file #{options[:config_file]}"
+      end
+
       [:concurrency, :timeout].each do |opt|
         raise ArgumentError, "#{opt}: #{options[opt]} is not a valid value" if options.has_key?(opt) && options[opt].to_i <= 0
       end

test/test_cli.rb

@@ -260,6 +260,14 @@ class TestCLI < Minitest::Test
           exit = assert_raises(SystemExit) { @cli.parse(%w[sidekiq -r ./test/fixtures]) }
           assert_equal 1, exit.status
         end
+
+        describe 'when config file path does not exist' do
+          it 'raises argument error' do
+            assert_raises(ArgumentError) do
+              @cli.parse(%w[sidekiq -r ./test/fake_env.rb -C /non/existent/path])
+            end
+          end
+        end
       end
     end
   end