delete Docker containers after code execution

lib/docker_client.rb

@@ -68,6 +68,7 @@ class DockerClient
         PortPool.release(port)
       end
     end
+    container.delete(force: true)
   end
 
   def execute_command(command, &block)

spec/lib/docker_client_spec.rb

@@ -98,9 +98,12 @@ describe DockerClient, docker: true do
 
     it 'releases allocated ports' do
       expect(container).to receive(:json).at_least(:once).and_return({'HostConfig' => {'PortBindings' => {foo: [{'HostPort' => '42'}]}}})
-      docker_client.send(:start_container, container)
       expect(PortPool).to receive(:release)
     end
+
+    it 'deletes the container' do
+      expect(container).to receive(:delete)
+    end
   end
 
   describe '#execute_command' do