extended Docker::Container with utility methods

config/initializers/mixins.rb

@@ -0,0 +1 @@
+Docker::Container::send(:include, DockerContainerMixin)

lib/docker_client.rb

@@ -62,12 +62,10 @@ class DockerClient
 
   def self.destroy_container(container)
     container.stop.kill
-    if container.json['HostConfig']['PortBindings']
-      container.json['HostConfig']['PortBindings'].values.each do |configuration|
+    (container.port_bindings.try(:values) || []).each do |configuration|
       port = configuration.first['HostPort'].to_i
       PortPool.release(port)
     end
-    end
     container.delete(force: true)
   end
 

lib/docker_container_mixin.rb

@@ -0,0 +1,9 @@
+module DockerContainerMixin
+  def binds
+    json['HostConfig']['Binds']
+  end
+
+  def port_bindings
+    json['HostConfig']['PortBindings']
+  end
+end

spec/lib/docker_container_mixin_spec.rb

@@ -0,0 +1,11 @@
+require 'rails_helper'
+
+describe DockerContainerMixin do
+  [:binds, :port_bindings].each do |method|
+    describe "##{method}" do
+      it 'is defined for Docker::Container' do
+        expect(Docker::Container.instance_methods).to include(method)
+      end
+    end
+  end
+end