Add specs for VariableDuplicates validator

spec/validators/variable_duplicates_validator_spec.rb

+require 'spec_helper'
+
+describe VariableDuplicatesValidator do
+  let(:validator) { described_class.new(attributes: [:variables], **options) }
+
+  describe '#validate_each' do
+    let(:project) { build(:project) }
+
+    subject { validator.validate_each(project, :variables, project.variables) }
+
+    context 'with no scope' do
+      let(:options) { {} }
+      let(:variables) { build_list(:ci_variable, 2, project: project) }
+
+      before do
+        project.variables << variables
+      end
+
+      it 'does not have any errors' do
+        subject
+
+        expect(project.errors.empty?).to be true
+      end
+
+      context 'with duplicates' do
+        before do
+          project.variables.build(key: variables.first.key, value: 'dummy_value')
+        end
+
+        it 'has a duplicate key error' do
+          subject
+
+          expect(project.errors[:variables]).to include("Duplicate variables: #{project.variables.last.key}")
+        end
+      end
+    end
+
+    context 'with a scope attribute' do
+      let(:options) { { scope: :environment_scope } }
+      let(:first_variable) { build(:ci_variable, key: 'test_key', environment_scope: '*', project: project) }
+      let(:second_variable) { build(:ci_variable, key: 'test_key', environment_scope: 'prod', project: project) }
+
+      before do
+        project.variables << first_variable
+        project.variables << second_variable
+      end
+
+      it 'does not have any errors' do
+        subject
+
+        expect(project.errors.empty?).to be true
+      end
+
+      context 'with duplicates' do
+        before do
+          project.variables.build(key: second_variable.key, value: 'dummy_value', environment_scope: second_variable.environment_scope)
+        end
+
+        it 'has a duplicate key error' do
+          subject
+
+          expect(project.errors[:variables]).to include("Duplicate variables: #{project.variables.last.key}")
+        end
+      end
+    end
+  end
+end