Improve CI stage configuration entry validations

lib/gitlab/ci/config/node/stage.rb

@@ -10,14 +10,16 @@ module Gitlab
 
           validations do
             validates :config, type: String
-            validates :global, required_attribute: true
-            validate :known_stage, on: :processed
 
-            def known_stage
+            with_options on: :processed do
+              validates :global, required: true
+
+              validate do
                 unless known?
-                stages_list = global.stages.join(', ')
                   errors.add(:config,
-                           "should be one of defined stages (#{stages_list})")
+                             'should be one of defined stages ' \
+                             "(#{global.stages.join(', ')})")
+                end
               end
             end
           end

lib/gitlab/ci/config/node/validators.rb

@@ -33,7 +33,7 @@ module Gitlab
             end
           end
 
-          class RequiredAttributeValidator < ActiveModel::EachValidator
+          class RequiredValidator < ActiveModel::EachValidator
             def validate_each(record, attribute, value)
               if value.nil?
                 raise Entry::InvalidError,

spec/lib/gitlab/ci/config/node/stage_spec.rb

@@ -28,10 +28,10 @@ describe Gitlab::Ci::Config::Node::Stage do
     context 'when stage config is incorrect' do
       describe '#errors' do
         context 'when reference to global node is not set' do
-          let(:stage) { described_class.new(config) }
+          let(:stage) { described_class.new('test') }
 
           it 'raises error' do
-            expect { stage }.to raise_error(
+            expect { stage.validate! }.to raise_error(
               Gitlab::Ci::Config::Node::Entry::InvalidError,
               /Entry needs global attribute set internally./
             )