add mailing clone api

lib/crm/mailing.rb

@@ -19,6 +19,16 @@ class Mailing < Core::BasicResource
     # @!parse extend Core::Mixins::Modifiable::ClassMethods
     # @!parse extend Core::Mixins::Searchable::ClassMethods
 
+    # Clones a mailing.
+    # @example
+    #   mailing.clone
+    #   # => Crm::Mailing
+    # @return [BasicResource] the cloned mailing.
+    # @api public
+    def clone
+      self.class.new(Core::RestApi.instance.post("#{path}/clone", {}))
+    end
+
     # Renders a preview of the email for the given contact.
     # @example
     #   mailing.html_body

spec/crm/mailing_spec.rb

@@ -40,6 +40,17 @@ module Crm
     end
   end
 
+  describe '#create' do
+    let(:mailing) { Mailing.new("id" => "abc") }
+
+    it 'clones a mailing' do
+      expect(Core::RestApi.instance).to receive(:post).with('mailings/abc/clone', {})
+        .and_return({"id" => "def"})
+      clone = mailing.clone
+      expect(clone.id).to eq('def')
+    end
+  end
+
   describe '#render_preview' do
     let(:mailing) { Mailing.new("id" => "abc") }
     let(:preview_output) {

spec/features/mailing_feature_spec.rb

@@ -101,6 +101,21 @@
     end
   end
 
+  describe 'clone' do
+    let(:mailing) do
+      Crm::Mailing.create({
+        title: 'My Mailing',
+        type_id: 'newsletter',
+      })
+    end
+
+    it 'clones the mailing' do
+      clone = mailing.clone
+      expect(clone.id).not_to eq(mailing.id)
+      expect(clone.title).to eq('My Mailing (Copy)')
+    end
+  end
+
   describe 'changes' do
     let(:mailing) do
       Crm::Mailing.create({