Extract base mapper

lib/gitlab/import/github/mapper/base.rb

+module Gitlab
+  module Import
+    module Github
+      module Mapper
+        class Base
+          def initialize(project, client)
+            @project = project
+            @client  = client
+          end
+
+          def each
+            return enum_for(:each) unless block_given?
+
+            method = klass.to_s.underscore.pluralize
+
+            client.public_send(method).each do |raw|
+              yield(klass.new(attributes_for(raw)))
+            end
+          end
+
+          private
+
+          attr_reader :project, :client
+
+          def attributes_for
+            {}
+          end
+
+          def klass
+            raise NotImplementedError,
+              "#{self.class} does not implement #{__method__}"
+          end
+        end
+      end
+    end
+  end
+end

lib/gitlab/import/github/mapper/label.rb

@@ -2,29 +2,20 @@ module Gitlab
   module Import
     module Github
       module Mapper
-        class Label
-          def initialize(project, client)
-            @project = project
-            @client  = client
-          end
-
-          def each
-            return enum_for(:each) unless block_given?
-
-            client.labels.each do |raw|
-              label = ::Label.new(
-                project: project,
-                title: raw.name,
-                color: "##{raw.color}"
-              )
-              yield(label)
-            end
+        class Label < Base
+          private
+          def attributes_for(raw)
+            {
+              project: project,
+              title: raw.name,
+              color: "##{raw.color}"
+            }
           end
-          private
-
-          attr_reader :project, :client
+          def klass
+            ::Label
+          end
         end
       end
     end

lib/gitlab/import/github/mapper/milestone.rb

@@ -2,34 +2,25 @@ module Gitlab
   module Import
     module Github
       module Mapper
-        class Milestone
-          def initialize(project, client)
-            @project = project
-            @client  = client
-          end
-
-          def each
-            return enum_for(:each) unless block_given?
-
-            client.milestones.each do |raw|
-              milestone = ::Milestone.new(
-                iid: raw.number,
-                project: project,
-                title: raw.title,
-                description: raw.description,
-                due_date: raw.due_on,
-                state: raw.state == 'closed' ? 'closed' : 'active',
-                created_at: raw.created_at,
-                updated_at: raw.state == 'closed' ? raw.closed_at : raw.updated_at
-              )
-              yield(milestone)
-            end
+        class Milestone < Base
+          private
+          def attributes_for(raw)
+            {
+              iid: raw.number,
+              project: project,
+              title: raw.title,
+              description: raw.description,
+              due_date: raw.due_on,
+              state: raw.state == 'closed' ? 'closed' : 'active',
+              created_at: raw.created_at,
+              updated_at: raw.state == 'closed' ? raw.closed_at : raw.updated_at
+            }
           end
-          private
-
-          attr_reader :project, :client
+          def klass
+            ::Milestone
+          end
         end
       end
     end

spec/lib/gitlab/import/github/mapper/base_spec.rb

+require 'spec_helper'
+
+describe Gitlab::Import::Github::Mapper::Base, lib: true do
+  let(:project) { double }
+  let(:client)  { double }
+
+  subject(:mapper) do
+    klass = Class.new(described_class)
+    klass.new(project, client)
+  end
+
+  describe '#each' do
+    context 'when klass is not implemented' do
+      it 'raises NotImplementedError' do
+        expect { mapper.each(&:to_s) }.to raise_error(NotImplementedError)
+      end
+    end
+  end
+end

spec/lib/gitlab/import/github/mapper/label_spec.rb

 require 'spec_helper'
 describe Gitlab::Import::Github::Mapper::Label, lib: true do
-  let(:project) { create(:empty_project) }
+  let(:project) { build(:empty_project) }
   let(:client)  { double(labels: response) }
   let(:response) do

spec/lib/gitlab/import/github/mapper/milestone_spec.rb

 require 'spec_helper'
 describe Gitlab::Import::Github::Mapper::Milestone, lib: true do
-  let(:project) { create(:empty_project) }
+  let(:project) { build(:empty_project) }
   let(:client)  { double(milestones: response) }
   let(:response) do