Add spec for migration

spec/migrations/20201027002551_migrate_services_to_http_integrations_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+require Rails.root.join('db', 'migrate', '20201027002551_migrate_services_to_http_integrations.rb')
+
+RSpec.describe MigrateServicesToHttpIntegrations do
+  let_it_be(:namespace) { table(:namespaces).create!(name: 'namespace', path: 'namespace') }
+  let_it_be(:project) { table(:projects).create!(id: 1, namespace_id: namespace.id) }
+  let_it_be(:alert_service) { table(:services).create(type: 'AlertsService', project_id: project.id)}
+  let_it_be(:alert_service_data) { table(:alerts_service_data).create(service_id: alert_service.id, encrypted_token: 'test', encrypted_token_iv: 'test')}
+
+  let(:http_integrations) { table(:alert_management_http_integrations) }
+
+  describe '#up' do
+    it 'creates the http integrations from the alert services', :aggregate_failures do
+      expect { migrate! }.to change { http_integrations.count }.by(1)
+
+      http_integration = http_integrations.last
+      expect(http_integration.project_id).to eq(alert_service.project_id)
+      expect(http_integration.encrypted_token).to eq(alert_service_data.encrypted_token)
+      expect(http_integration.encrypted_token_iv).to eq(alert_service_data.encrypted_token_iv)
+      expect(http_integration.active).to eq(alert_service.active)
+      expect(http_integration.name).to eq(described_class::SERVICE_NAMES_IDENTIFIER[:name])
+      expect(http_integration.endpoint_identifier).to eq(described_class::SERVICE_NAMES_IDENTIFIER[:identifier])
+    end
+  end
+end